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Groups > linux.kernel > #1358095 > unrolled thread
| Started by | Ming Lei <ming.lei@canonical.com> |
|---|---|
| First post | 2016-03-15 16:10 +0100 |
| Last post | 2016-03-17 07:00 +0100 |
| Articles | 11 — 2 participants |
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Re: Possible race at user mode helper in request_firmware Ming Lei <ming.lei@canonical.com> - 2016-03-15 16:10 +0100
Re: Possible race at user mode helper in request_firmware Ming Lei <ming.lei@canonical.com> - 2016-03-16 03:10 +0100
Re: Possible race at user mode helper in request_firmware Chandra Sekhar Lingutla <clingutla@codeaurora.org> - 2016-03-16 08:10 +0100
Re: Possible race at user mode helper in request_firmware Ming Lei <ming.lei@canonical.com> - 2016-03-16 09:20 +0100
Re: Possible race at user mode helper in request_firmware Ming Lei <ming.lei@canonical.com> - 2016-03-16 09:50 +0100
Re: Possible race at user mode helper in request_firmware Chandra Sekhar Lingutla <clingutla@codeaurora.org> - 2016-03-16 09:50 +0100
Re: Possible race at user mode helper in request_firmware Ming Lei <ming.lei@canonical.com> - 2016-03-16 10:00 +0100
Re: Possible race at user mode helper in request_firmware Chandra Sekhar Lingutla <clingutla@codeaurora.org> - 2016-03-16 10:10 +0100
Re: Possible race at user mode helper in request_firmware Chandra Sekhar Lingutla <clingutla@codeaurora.org> - 2016-03-16 11:00 +0100
Re: Possible race at user mode helper in request_firmware Ming Lei <ming.lei@canonical.com> - 2016-03-16 11:30 +0100
Re: Possible race at user mode helper in request_firmware Chandra Sekhar Lingutla <clingutla@codeaurora.org> - 2016-03-17 07:00 +0100
| From | Ming Lei <ming.lei@canonical.com> |
|---|---|
| Date | 2016-03-15 16:10 +0100 |
| Subject | Re: Possible race at user mode helper in request_firmware |
| Message-ID | <rcYLE-3Jo-19@gated-at.bofh.it> |
Hi,
On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
> Hello,
>
> I see possible race in _request_firmware_load function, on which I wanted to
> take your opinion.
>
> When system is going to low power mode, device_cache_fw_images() is called
> from pm notifier which schedules asynchronous workers to cache devices
> firmware.
> If more than 2 async requests falls under user helper mode, then there is a
> use after free of "firmware" directory kobject.
If two requests are for getting same firmware image, only one can be sent
out and be completed with user helper, please see fw_lookup_and_allocate_buf(),
so the race shouldn't have been triggered in this case.
So I guess your test must be involved with at least two different requests.
>
> The race will hit, when one asynchronous worker calls device_del() while
> other asynchronous worker calls get_device_parent() in
> _request_firmware_load().
> After loading firmware, first worker calls device_del(), and "firmware"
> directory ref count is 1, so cleanup_glue_dir() calls kobject_put() with
> gdp_mutex lock held.
> Meanwhile, second async worker calls device_add(), and get_device_parent()
> is still able to find the firmware directory kobject in ksets after getting
> gdp_mutex.
> This kobject gets added as parent to the second device kobject.
> By the time of accessing the parent kobject, its ref count was 0 and prints
> below warning stack followed by crash.
The trick here is just that we don't use 'struct device' in
device_cache_fw_images(),
then the firmware device's parent is null during calling device_add() from
_request_firmware_load(), but this should be allowed by driver core.
From firmware class view, both device_add()/device_del() is run with pair,
and driver core still complains during get_device_parent(), so something
inside driver core should be be wrong, IMO.
>
> [21147.455038] ------------[ cut here ]------------
> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
> kobject_get+0x50/0x68()
> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
> qcrypto_module(O)
> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
> 3.10.84-g0957845-00427-g56a05c2 #1
> [21147.481284] Workqueue: events_unbound async_run_entry_fn
> [21147.481296] Call trace:
> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
> [21147.481490] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>
> [21147.486436] Unable to handle kernel paging request at virtual address
> 0x6b6b6b6b6b6b6bcb
> [21147.493816] pgd = ffffffc0a982d000
> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
> qcrypto_module(O)
> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
> 3.10.84-g0957845-00427-g56a05c2 #1
> [21147.524686] Workqueue: events_unbound async_run_entry_fn
> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
> ffffffc007880000
> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>] pstate:
> 80000145
> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
> 0xffffffc007880058)
> [21148.003673] Call trace:
> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
> [21148.044822] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>
> Below is the callstack where the parent is freed from the slub_debug info.
> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
> 0xFFFFFFC00061C524 \\vmlinux\firmware_class\_request_firmware\out+0x71C
> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
> 0xFFFFFFC00061C65C \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>
> For similar type of issue, I see there is an existing fix: "sysfs: driver
> core: Fix glue dir race condition by gdp_mutex".
> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>
> Still I am able to reproduce the issue. I have verified this race on
> kernels: 3.10, 3.18 and 4.4.
>
> I followed below procedure to reproduce the issue:
> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
> 2. Use test_firmware, modified the test for async calls
> 3. Replace WARN_ON with BUG_ON in kref_get().
> I ran below script from shell:
> count=0
> while [ 1 ]
> do
> echo 3 > /sys/devices/virtual/misc/test_firmware/trigger_ufw
> if [ $? -ne 0 ]; then
> print "Exiting.. "
> exit 1
> fi
> count=$(($count +1))
> echo "count $count"
> done
>
> With below patch, I could reproduce the issue in the 2nd iteration.
I will run your test script to see if there is new findings.
>
> -------------------------8<----------------------------------------------
>
> To reproduce the race condition, use firmware test and
> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
> releases. So that we can catch the bug easily.
>
> Enabled below flags in kernel config file:
>
> +CONFIG_DEBUG_KOBJECT_RELEASE=y
> +CONFIG_TEST_FIRMWARE=y
Looks I can't reproduce the issue with your approach.
>
>
> diff --git a/include/linux/kref.h b/include/linux/kref.h
> index 484604d..727fb24 100644
> --- a/include/linux/kref.h
> +++ b/include/linux/kref.h
> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
> * condition when this kref is freeing by some other thread right
> now.
> * In this case one should use kref_get_unless_zero()
> */
> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
> }
>
> /**
> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
> old mode 100644
> new mode 100755
> index 86374c1..14c9598
> --- a/lib/test_firmware.c
> +++ b/lib/test_firmware.c
> @@ -18,6 +18,7 @@
> #include <linux/miscdevice.h>
> #include <linux/slab.h>
> #include <linux/uaccess.h>
> +#include <linux/async.h>
>
> +
> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
> +
> +static void __async_ufw_work(void *name,
> + async_cookie_t cookie)
> +{
> + const struct firmware *fw;
> + const char *fw_name = name;
> + int ret;
> +
> + pr_err("requesting %s\n", fw_name);
> +
> + ret = request_firmware(&fw, fw_name, NULL);
> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
> + if (!ret)
> + kfree(fw);
> +
> +}
> +
> +static char *name[] = { "fw1.bin", "fw2.bin"};
> +
> +static ssize_t trigger_ufw_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int rc, i, c=0;
> + u32 start;
> + char *fw_name;
> +
> + rc = kstrtou32(buf, 0, &start);
> + if (rc){
> + pr_err("Invalid option\n");
> + return rc;
> + }
> + pr_err(" no of iterations %d\n", start);
> +
> + for (i=0; i< start; i++)
> + {
> + if (c >= 2)
> + c = 0;
> + fw_name = name[c++];
> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
> &ufw_domain);
> + }
> + async_synchronize_full_domain(&ufw_domain);
> + return count;
> +}
>
> static DEVICE_ATTR_WO(trigger_request);
> +static DEVICE_ATTR_WO(trigger_ufw);
>
> static int __init test_firmware_init(void)
> {
> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
> goto dereg;
> }
>
> + rc = device_create_file(test_fw_misc_device.this_device,
> + &dev_attr_trigger_ufw);
> + if (rc) {
> + pr_err("could not create sysfs interface: %d\n", rc);
> + goto dereg;
> + }
> pr_warn("interface ready\n");
>
> return 0;
> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
> {
> release_firmware(test_firmware);
> device_remove_file(test_fw_misc_device.this_device,
> - &dev_attr_trigger_request);
> + &dev_attr_trigger_request);
> + device_remove_file(test_fw_misc_device.this_device,
> + &dev_attr_trigger_ufw);
> misc_deregister(&test_fw_misc_device);
> pr_warn("removed interface\n");
> }
>
> ----------------------------8<--------------------------------------------
>
> Thanks and regards,
> Chandrasekhar L.
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of
> Code Aurora Forum,
> a Linux Foundation Collaborative Project.
[toc] | [next] | [standalone]
| From | Ming Lei <ming.lei@canonical.com> |
|---|---|
| Date | 2016-03-16 03:10 +0100 |
| Message-ID | <rd94m-2i7-13@gated-at.bofh.it> |
| In reply to | #1358095 |
On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@canonical.com> wrote:
> Hi,
>
> On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
>> Hello,
>>
>> I see possible race in _request_firmware_load function, on which I wanted to
>> take your opinion.
>>
>> When system is going to low power mode, device_cache_fw_images() is called
>> from pm notifier which schedules asynchronous workers to cache devices
>> firmware.
>> If more than 2 async requests falls under user helper mode, then there is a
>> use after free of "firmware" directory kobject.
>
> If two requests are for getting same firmware image, only one can be sent
> out and be completed with user helper, please see fw_lookup_and_allocate_buf(),
> so the race shouldn't have been triggered in this case.
>
> So I guess your test must be involved with at least two different requests.
>
>>
>> The race will hit, when one asynchronous worker calls device_del() while
>> other asynchronous worker calls get_device_parent() in
>> _request_firmware_load().
>> After loading firmware, first worker calls device_del(), and "firmware"
>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put() with
>> gdp_mutex lock held.
>> Meanwhile, second async worker calls device_add(), and get_device_parent()
>> is still able to find the firmware directory kobject in ksets after getting
>> gdp_mutex.
>> This kobject gets added as parent to the second device kobject.
>> By the time of accessing the parent kobject, its ref count was 0 and prints
>> below warning stack followed by crash.
>
> The trick here is just that we don't use 'struct device' in
> device_cache_fw_images(),
> then the firmware device's parent is null during calling device_add() from
> _request_firmware_load(), but this should be allowed by driver core.
>
> From firmware class view, both device_add()/device_del() is run with pair,
> and driver core still complains during get_device_parent(), so something
> inside driver core should be be wrong, IMO.
Thinking about the issue further, I believe it is a false positive which is
caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
1) device_add() path
get_device_parent()
......
mutex_lock(&gdp_mutex);
/* find our class-directory at the parent and reference it */
spin_lock(&dev->class->p->glue_dirs.list_lock);
list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
if (k->parent == parent_kobj) {
kobj = kobject_get(k);
break;
}
spin_unlock(&dev->class->p->glue_dirs.list_lock);
if (kobj) {
mutex_unlock(&gdp_mutex);
return kobj;
}
k = class_dir_create_and_add(dev->class, parent_kobj);
mutex_unlock(&gdp_mutex);
......
2) device_del() path
cleanup_device_parent()
->cleanup_glue_dir()
->mutex_lock(&gdp_mutex);
->kobject_put(glue_dir);
->kobject_cleanup()
->kobject_del()
->kobj_kset_leave()
->mutex_unlock(&gdp_mutex);
So gdp_mutex is held wrt. both looking up/adding the parent kobject
and removing the parent kobject. Actually with this lock, both glur_dir
kobject's referece counting and joining/leaving kset are run atomically.
The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
which causes kobject_cleanup() to be run in workqueue context and the
lock of gdp_mutex can't be hold in that situation anymore. That is the root
cause for your race.
That also said DEBUG_KOBJECT_RELEASE might cause trouble in
some situations.
Thanks,
Ming
>
>>
>> [21147.455038] ------------[ cut here ]------------
>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
>> kobject_get+0x50/0x68()
>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
>> qcrypto_module(O)
>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>> 3.10.84-g0957845-00427-g56a05c2 #1
>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
>> [21147.481296] Call trace:
>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>> [21147.481490] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>>
>> [21147.486436] Unable to handle kernel paging request at virtual address
>> 0x6b6b6b6b6b6b6bcb
>> [21147.493816] pgd = ffffffc0a982d000
>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
>> qcrypto_module(O)
>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>> 3.10.84-g0957845-00427-g56a05c2 #1
>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
>> ffffffc007880000
>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>] pstate:
>> 80000145
>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
>> 0xffffffc007880058)
>> [21148.003673] Call trace:
>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>> [21148.044822] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>>
>> Below is the callstack where the parent is freed from the slub_debug info.
>> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
>> 0xFFFFFFC00061C524 \\vmlinux\firmware_class\_request_firmware\out+0x71C
>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
>> 0xFFFFFFC00061C65C \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>>
>> For similar type of issue, I see there is an existing fix: "sysfs: driver
>> core: Fix glue dir race condition by gdp_mutex".
>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>>
>> Still I am able to reproduce the issue. I have verified this race on
>> kernels: 3.10, 3.18 and 4.4.
>>
>> I followed below procedure to reproduce the issue:
>> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
>> 2. Use test_firmware, modified the test for async calls
>> 3. Replace WARN_ON with BUG_ON in kref_get().
>> I ran below script from shell:
>> count=0
>> while [ 1 ]
>> do
>> echo 3 > /sys/devices/virtual/misc/test_firmware/trigger_ufw
>> if [ $? -ne 0 ]; then
>> print "Exiting.. "
>> exit 1
>> fi
>> count=$(($count +1))
>> echo "count $count"
>> done
>>
>> With below patch, I could reproduce the issue in the 2nd iteration.
>
> I will run your test script to see if there is new findings.
>
>>
>> -------------------------8<----------------------------------------------
>>
>> To reproduce the race condition, use firmware test and
>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
>> releases. So that we can catch the bug easily.
>>
>> Enabled below flags in kernel config file:
>>
>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
>> +CONFIG_TEST_FIRMWARE=y
>
> Looks I can't reproduce the issue with your approach.
>
>>
>>
>> diff --git a/include/linux/kref.h b/include/linux/kref.h
>> index 484604d..727fb24 100644
>> --- a/include/linux/kref.h
>> +++ b/include/linux/kref.h
>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
>> * condition when this kref is freeing by some other thread right
>> now.
>> * In this case one should use kref_get_unless_zero()
>> */
>> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
>> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
>> }
>>
>> /**
>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>> old mode 100644
>> new mode 100755
>> index 86374c1..14c9598
>> --- a/lib/test_firmware.c
>> +++ b/lib/test_firmware.c
>> @@ -18,6 +18,7 @@
>> #include <linux/miscdevice.h>
>> #include <linux/slab.h>
>> #include <linux/uaccess.h>
>> +#include <linux/async.h>
>>
>> +
>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
>> +
>> +static void __async_ufw_work(void *name,
>> + async_cookie_t cookie)
>> +{
>> + const struct firmware *fw;
>> + const char *fw_name = name;
>> + int ret;
>> +
>> + pr_err("requesting %s\n", fw_name);
>> +
>> + ret = request_firmware(&fw, fw_name, NULL);
>> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
>> + if (!ret)
>> + kfree(fw);
>> +
>> +}
>> +
>> +static char *name[] = { "fw1.bin", "fw2.bin"};
>> +
>> +static ssize_t trigger_ufw_store(struct device *dev,
>> + struct device_attribute *attr,
>> + const char *buf, size_t count)
>> +{
>> + int rc, i, c=0;
>> + u32 start;
>> + char *fw_name;
>> +
>> + rc = kstrtou32(buf, 0, &start);
>> + if (rc){
>> + pr_err("Invalid option\n");
>> + return rc;
>> + }
>> + pr_err(" no of iterations %d\n", start);
>> +
>> + for (i=0; i< start; i++)
>> + {
>> + if (c >= 2)
>> + c = 0;
>> + fw_name = name[c++];
>> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
>> &ufw_domain);
>> + }
>> + async_synchronize_full_domain(&ufw_domain);
>> + return count;
>> +}
>>
>> static DEVICE_ATTR_WO(trigger_request);
>> +static DEVICE_ATTR_WO(trigger_ufw);
>>
>> static int __init test_firmware_init(void)
>> {
>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
>> goto dereg;
>> }
>>
>> + rc = device_create_file(test_fw_misc_device.this_device,
>> + &dev_attr_trigger_ufw);
>> + if (rc) {
>> + pr_err("could not create sysfs interface: %d\n", rc);
>> + goto dereg;
>> + }
>> pr_warn("interface ready\n");
>>
>> return 0;
>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
>> {
>> release_firmware(test_firmware);
>> device_remove_file(test_fw_misc_device.this_device,
>> - &dev_attr_trigger_request);
>> + &dev_attr_trigger_request);
>> + device_remove_file(test_fw_misc_device.this_device,
>> + &dev_attr_trigger_ufw);
>> misc_deregister(&test_fw_misc_device);
>> pr_warn("removed interface\n");
>> }
>>
>> ----------------------------8<--------------------------------------------
>>
>> Thanks and regards,
>> Chandrasekhar L.
>> --
>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of
>> Code Aurora Forum,
>> a Linux Foundation Collaborative Project.
[toc] | [prev] | [next] | [standalone]
| From | Chandra Sekhar Lingutla <clingutla@codeaurora.org> |
|---|---|
| Date | 2016-03-16 08:10 +0100 |
| Message-ID | <rddKG-5vq-11@gated-at.bofh.it> |
| In reply to | #1358474 |
Hi Ming,
On 03/16/2016 07:36 AM, Ming Lei wrote:
> On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@canonical.com> wrote:
>> Hi,
>>
>> On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
>>> Hello,
>>>
>>> I see possible race in _request_firmware_load function, on which I wanted to
>>> take your opinion.
>>>
>>> When system is going to low power mode, device_cache_fw_images() is called
>>> from pm notifier which schedules asynchronous workers to cache devices
>>> firmware.
>>> If more than 2 async requests falls under user helper mode, then there is a
>>> use after free of "firmware" directory kobject.
>>
>> If two requests are for getting same firmware image, only one can be sent
>> out and be completed with user helper, please see fw_lookup_and_allocate_buf(),
>> so the race shouldn't have been triggered in this case.
>>
>> So I guess your test must be involved with at least two different requests.
>>
>>>
>>> The race will hit, when one asynchronous worker calls device_del() while
>>> other asynchronous worker calls get_device_parent() in
>>> _request_firmware_load().
>>> After loading firmware, first worker calls device_del(), and "firmware"
>>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put() with
>>> gdp_mutex lock held.
>>> Meanwhile, second async worker calls device_add(), and get_device_parent()
>>> is still able to find the firmware directory kobject in ksets after getting
>>> gdp_mutex.
>>> This kobject gets added as parent to the second device kobject.
>>> By the time of accessing the parent kobject, its ref count was 0 and prints
>>> below warning stack followed by crash.
>>
>> The trick here is just that we don't use 'struct device' in
>> device_cache_fw_images(),
>> then the firmware device's parent is null during calling device_add() from
>> _request_firmware_load(), but this should be allowed by driver core.
>>
>> From firmware class view, both device_add()/device_del() is run with pair,
>> and driver core still complains during get_device_parent(), so something
>> inside driver core should be be wrong, IMO.
>
> Thinking about the issue further, I believe it is a false positive which is
> caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
>
> 1) device_add() path
>
> get_device_parent()
> ......
> mutex_lock(&gdp_mutex);
>
> /* find our class-directory at the parent and reference it */
> spin_lock(&dev->class->p->glue_dirs.list_lock);
> list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
> if (k->parent == parent_kobj) {
> kobj = kobject_get(k);
> break;
> }
> spin_unlock(&dev->class->p->glue_dirs.list_lock);
> if (kobj) {
> mutex_unlock(&gdp_mutex);
> return kobj;
> }
> k = class_dir_create_and_add(dev->class, parent_kobj);
> mutex_unlock(&gdp_mutex);
> ......
>
> 2) device_del() path
>
> cleanup_device_parent()
> ->cleanup_glue_dir()
> ->mutex_lock(&gdp_mutex);
> ->kobject_put(glue_dir);
> ->kobject_cleanup()
> ->kobject_del()
> ->kobj_kset_leave()
> ->mutex_unlock(&gdp_mutex);
>
> So gdp_mutex is held wrt. both looking up/adding the parent kobject
> and removing the parent kobject. Actually with this lock, both glur_dir
> kobject's referece counting and joining/leaving kset are run atomically.
>
> The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
> which causes kobject_cleanup() to be run in workqueue context and the
> lock of gdp_mutex can't be hold in that situation anymore. That is the root
> cause for your race.
>
> That also said DEBUG_KOBJECT_RELEASE might cause trouble in
> some situations.
>
> Thanks,
> Ming
>
I agree that, CONFIG_DEBUG_KOBJECT_RELEASE can cause the race, as it delays
call to kobject_cleanup() which deletes kobj entry in glue_dir list.
I see the race even after disabling CONFIG_DEBUG_KOBJECT_RELEASE.
The race is between kobject_put() and kobject_get() for the "firmware" directory.
In device_del() path, I see the race after the call of cleanup_device_parent().
cleanup_device_parent() calls kobject_put(glue_dir) with gdp_mutex lock holding,
So ideally, to call kobject_put/kobject_get(glue_dir) we need to acquire gdp_mutex.
but kobject_del(kobj) will not hold the gdp_mutex lock while calling kobject_put(kobj->parent).
Here is the race:
Consider 2 async works calls request_firmware() for 2 different binaries (fw1.bin, fw2.bin)
Async work1 got scheduled first, and it falls in user helper mode so it creates "firmware" dir
and then creates "fw1.bin" directory to load data from user.
After load completion or timeout, it starts cleanup dir's, meantime async work2 got scheduled and
it also falls in user helper mode, and story starts here:
PATH1 req fw for "fw1.bin" PATH2
req fw for "fw2.bin"
_request_firmware_load()
device_del(dev1)
->cleanup_device_parent()
mutex_lock(&gdp_mutex);
_request_firmware_load("fw2.bin")
kobject_put(kobj->parent); --> firmware ref ->1
->device_add(dev2)
mutex_unlock(&gdp_mutex); ->get_device_parent()
->kobject_del() mutex_lock(&gdp_mutex)
kobj_kset_leave(kobj); -->del "fw1.bin" kobj in kset list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
kobject_put(kobj->parent); /* No lock :)*/ if (k->parent == parent_kobj) {
->kref_put() --> firmware ref ->0 kobj = kobject_get(k); -> k is "firmware"
dir
->kboject_release() break;
->kobject_del() }
/*here deletes firmware entry in kset*/ mutex_unlock(&gdp_mutex)
->dev2->kobj.parent = kobj -> kobj is released already
PATH 1 is started removing the kobject of "fw1.bin" and its parent "firmware"
.
cleanup_device_parent(dev1) makes firmware ref count to 1, by calling kobject_put(firmware) with gdp_mutex held.
and kobject_del(dev1->kobj) will again calls kobject_put(kobj->parent) without holding gdp_mutex.
In PATH2, glue_dir is able to find "firmware" kobj, as firmware dir kobj is deleted from the glue_dir list at kboject_release().
and it calls kobject_get(firmware), by the time PATH1 calls kobject_release(firmware).
So PATH2 got reference of freed firmware kobj and added as parent to "fw2.bin" kobj.
I think, here is possible fix for this race:
------------------------8<-------------------------------------
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 5d8b713..47bc082 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1224,7 +1224,13 @@ void device_del(struct device *dev)
BUS_NOTIFY_REMOVED_DEVICE, dev);
kobject_uevent(&dev->kobj, KOBJ_REMOVE);
cleanup_device_parent(dev);
- kobject_del(&dev->kobj);
+
+ if (dev->kobj.parent->kset == &dev->class->p->glue_dirs) {
+ mutex_lock(&gdp_mutex);
+ kobject_del(&dev->kobj);
+ mutex_unlock(&gdp_mutex);
+ } else
+ kobject_del(&dev->kobj);
put_device(parent);
}
EXPORT_SYMBOL_GPL(device_del);
--------------------------->8-----------------------------------
>>
>>>
>>> [21147.455038] ------------[ cut here ]------------
>>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
>>> kobject_get+0x50/0x68()
>>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>> qcrypto_module(O)
>>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
>>> [21147.481296] Call trace:
>>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
>>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
>>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
>>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
>>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
>>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
>>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
>>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
>>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>> [21147.481490] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
>>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
>>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>>>
>>> [21147.486436] Unable to handle kernel paging request at virtual address
>>> 0x6b6b6b6b6b6b6bcb
>>> [21147.493816] pgd = ffffffc0a982d000
>>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
>>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>> qcrypto_module(O)
>>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
>>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
>>> ffffffc007880000
>>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
>>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
>>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>] pstate:
>>> 80000145
>>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
>>> 0xffffffc007880058)
>>> [21148.003673] Call trace:
>>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
>>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
>>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
>>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
>>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>> [21148.044822] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
>>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
>>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
>>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>>>
>>> Below is the callstack where the parent is freed from the slub_debug info.
>>> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
>>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
>>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
>>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
>>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
>>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
>>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
>>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
>>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
>>> 0xFFFFFFC00061C524 \\vmlinux\firmware_class\_request_firmware\out+0x71C
>>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
>>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
>>> 0xFFFFFFC00061C65C \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
>>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
>>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
>>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
>>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>>>
>>> For similar type of issue, I see there is an existing fix: "sysfs: driver
>>> core: Fix glue dir race condition by gdp_mutex".
>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>>>
>>> Still I am able to reproduce the issue. I have verified this race on
>>> kernels: 3.10, 3.18 and 4.4.
>>>
>>> I followed below procedure to reproduce the issue:
>>> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
>>> 2. Use test_firmware, modified the test for async calls
>>> 3. Replace WARN_ON with BUG_ON in kref_get().
>>> I ran below script from shell:
>>> count=0
>>> while [ 1 ]
>>> do
>>> echo 3 > /sys/devices/virtual/misc/test_firmware/trigger_ufw
>>> if [ $? -ne 0 ]; then
>>> print "Exiting.. "
>>> exit 1
>>> fi
>>> count=$(($count +1))
>>> echo "count $count"
>>> done
>>>
>>> With below patch, I could reproduce the issue in the 2nd iteration.
>>
>> I will run your test script to see if there is new findings.
>>
>>>
>>> -------------------------8<----------------------------------------------
>>>
>>> To reproduce the race condition, use firmware test and
>>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
>>> releases. So that we can catch the bug easily.
>>>
>>> Enabled below flags in kernel config file:
>>>
>>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
>>> +CONFIG_TEST_FIRMWARE=y
>>
>> Looks I can't reproduce the issue with your approach.
>>
>>>
>>>
>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
>>> index 484604d..727fb24 100644
>>> --- a/include/linux/kref.h
>>> +++ b/include/linux/kref.h
>>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
>>> * condition when this kref is freeing by some other thread right
>>> now.
>>> * In this case one should use kref_get_unless_zero()
>>> */
>>> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
>>> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
>>> }
>>>
>>> /**
>>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>>> old mode 100644
>>> new mode 100755
>>> index 86374c1..14c9598
>>> --- a/lib/test_firmware.c
>>> +++ b/lib/test_firmware.c
>>> @@ -18,6 +18,7 @@
>>> #include <linux/miscdevice.h>
>>> #include <linux/slab.h>
>>> #include <linux/uaccess.h>
>>> +#include <linux/async.h>
>>>
>>> +
>>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
>>> +
>>> +static void __async_ufw_work(void *name,
>>> + async_cookie_t cookie)
>>> +{
>>> + const struct firmware *fw;
>>> + const char *fw_name = name;
>>> + int ret;
>>> +
>>> + pr_err("requesting %s\n", fw_name);
>>> +
>>> + ret = request_firmware(&fw, fw_name, NULL);
>>> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
>>> + if (!ret)
>>> + kfree(fw);
>>> +
>>> +}
>>> +
>>> +static char *name[] = { "fw1.bin", "fw2.bin"};
>>> +
>>> +static ssize_t trigger_ufw_store(struct device *dev,
>>> + struct device_attribute *attr,
>>> + const char *buf, size_t count)
>>> +{
>>> + int rc, i, c=0;
>>> + u32 start;
>>> + char *fw_name;
>>> +
>>> + rc = kstrtou32(buf, 0, &start);
>>> + if (rc){
>>> + pr_err("Invalid option\n");
>>> + return rc;
>>> + }
>>> + pr_err(" no of iterations %d\n", start);
>>> +
>>> + for (i=0; i< start; i++)
>>> + {
>>> + if (c >= 2)
>>> + c = 0;
>>> + fw_name = name[c++];
>>> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
>>> &ufw_domain);
>>> + }
>>> + async_synchronize_full_domain(&ufw_domain);
>>> + return count;
>>> +}
>>>
>>> static DEVICE_ATTR_WO(trigger_request);
>>> +static DEVICE_ATTR_WO(trigger_ufw);
>>>
>>> static int __init test_firmware_init(void)
>>> {
>>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
>>> goto dereg;
>>> }
>>>
>>> + rc = device_create_file(test_fw_misc_device.this_device,
>>> + &dev_attr_trigger_ufw);
>>> + if (rc) {
>>> + pr_err("could not create sysfs interface: %d\n", rc);
>>> + goto dereg;
>>> + }
>>> pr_warn("interface ready\n");
>>>
>>> return 0;
>>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
>>> {
>>> release_firmware(test_firmware);
>>> device_remove_file(test_fw_misc_device.this_device,
>>> - &dev_attr_trigger_request);
>>> + &dev_attr_trigger_request);
>>> + device_remove_file(test_fw_misc_device.this_device,
>>> + &dev_attr_trigger_ufw);
>>> misc_deregister(&test_fw_misc_device);
>>> pr_warn("removed interface\n");
>>> }
>>>
>>> ----------------------------8<--------------------------------------------
>>>
>>> Thanks and regards,
>>> Chandrasekhar L.
>>> --
>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of
>>> Code Aurora Forum,
>>> a Linux Foundation Collaborative Project.
[toc] | [prev] | [next] | [standalone]
| From | Ming Lei <ming.lei@canonical.com> |
|---|---|
| Date | 2016-03-16 09:20 +0100 |
| Message-ID | <rdeQr-6eY-47@gated-at.bofh.it> |
| In reply to | #1358563 |
Hi Chandra,
On Wed, Mar 16, 2016 at 3:02 PM, Chandra Sekhar Lingutla
<clingutla@codeaurora.org> wrote:
> Hi Ming,
>
>
> On 03/16/2016 07:36 AM, Ming Lei wrote:
>>
>> On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@canonical.com> wrote:
>>>
>>> Hi,
>>>
>>> On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
>>>>
>>>> Hello,
>>>>
>>>> I see possible race in _request_firmware_load function, on which I
>>>> wanted to
>>>> take your opinion.
>>>>
>>>> When system is going to low power mode, device_cache_fw_images() is
>>>> called
>>>> from pm notifier which schedules asynchronous workers to cache devices
>>>> firmware.
>>>> If more than 2 async requests falls under user helper mode, then there
>>>> is a
>>>> use after free of "firmware" directory kobject.
>>>
>>>
>>> If two requests are for getting same firmware image, only one can be sent
>>> out and be completed with user helper, please see
>>> fw_lookup_and_allocate_buf(),
>>> so the race shouldn't have been triggered in this case.
>>>
>>> So I guess your test must be involved with at least two different
>>> requests.
>>>
>>>>
>>>> The race will hit, when one asynchronous worker calls device_del() while
>>>> other asynchronous worker calls get_device_parent() in
>>>> _request_firmware_load().
>>>> After loading firmware, first worker calls device_del(), and "firmware"
>>>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put() with
>>>> gdp_mutex lock held.
>>>> Meanwhile, second async worker calls device_add(), and
>>>> get_device_parent()
>>>> is still able to find the firmware directory kobject in ksets after
>>>> getting
>>>> gdp_mutex.
>>>> This kobject gets added as parent to the second device kobject.
>>>> By the time of accessing the parent kobject, its ref count was 0 and
>>>> prints
>>>> below warning stack followed by crash.
>>>
>>>
>>> The trick here is just that we don't use 'struct device' in
>>> device_cache_fw_images(),
>>> then the firmware device's parent is null during calling device_add()
>>> from
>>> _request_firmware_load(), but this should be allowed by driver core.
>>>
>>> From firmware class view, both device_add()/device_del() is run with
>>> pair,
>>> and driver core still complains during get_device_parent(), so something
>>> inside driver core should be be wrong, IMO.
>>
>>
>> Thinking about the issue further, I believe it is a false positive which
>> is
>> caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
>>
>> 1) device_add() path
>>
>> get_device_parent()
>> ......
>> mutex_lock(&gdp_mutex);
>>
>> /* find our class-directory at the parent and reference
>> it */
>> spin_lock(&dev->class->p->glue_dirs.list_lock);
>> list_for_each_entry(k, &dev->class->p->glue_dirs.list,
>> entry)
>> if (k->parent == parent_kobj) {
>> kobj = kobject_get(k);
>> break;
>> }
>> spin_unlock(&dev->class->p->glue_dirs.list_lock);
>> if (kobj) {
>> mutex_unlock(&gdp_mutex);
>> return kobj;
>> }
>> k = class_dir_create_and_add(dev->class, parent_kobj);
>> mutex_unlock(&gdp_mutex);
>> ......
>>
>> 2) device_del() path
>>
>> cleanup_device_parent()
>> ->cleanup_glue_dir()
>> ->mutex_lock(&gdp_mutex);
>> ->kobject_put(glue_dir);
>> ->kobject_cleanup()
>> ->kobject_del()
>> ->kobj_kset_leave()
>> ->mutex_unlock(&gdp_mutex);
>>
>> So gdp_mutex is held wrt. both looking up/adding the parent kobject
>> and removing the parent kobject. Actually with this lock, both glur_dir
>> kobject's referece counting and joining/leaving kset are run atomically.
>>
>> The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
>> which causes kobject_cleanup() to be run in workqueue context and the
>> lock of gdp_mutex can't be hold in that situation anymore. That is the
>> root
>> cause for your race.
>>
>> That also said DEBUG_KOBJECT_RELEASE might cause trouble in
>> some situations.
>>
>> Thanks,
>> Ming
>>
> I agree that, CONFIG_DEBUG_KOBJECT_RELEASE can cause the race, as it delays
> call to kobject_cleanup() which deletes kobj entry in glue_dir list.
>
> I see the race even after disabling CONFIG_DEBUG_KOBJECT_RELEASE.
>
> The race is between kobject_put() and kobject_get() for the "firmware"
> directory.
Could you provide the kernel warning or sort of log about the race by
disabling CONFIG_DEBUG_KOBJECT_RELEASE?
>
> In device_del() path, I see the race after the call of
> cleanup_device_parent().
> cleanup_device_parent() calls kobject_put(glue_dir) with gdp_mutex lock
> holding,
> So ideally, to call kobject_put/kobject_get(glue_dir) we need to acquire
> gdp_mutex.
I don't think so, it is the responsibility of kobject_get() caller to make sure
the kobject isn't released yet.
>
> but kobject_del(kobj) will not hold the gdp_mutex lock while calling
> kobject_put(kobj->parent).
>
> Here is the race:
>
> Consider 2 async works calls request_firmware() for 2 different binaries
> (fw1.bin, fw2.bin)
> Async work1 got scheduled first, and it falls in user helper mode so it
> creates "firmware" dir
> and then creates "fw1.bin" directory to load data from user.
> After load completion or timeout, it starts cleanup dir's, meantime async
> work2 got scheduled and
> it also falls in user helper mode, and story starts here:
>
> PATH1 req fw for "fw1.bin" PATH2
> req fw for "fw2.bin"
> _request_firmware_load()
> device_del(dev1)
>
> ->cleanup_device_parent()
>
> mutex_lock(&gdp_mutex);
> _request_firmware_load("fw2.bin")
> kobject_put(kobj->parent); --> firmware ref ->1
> ->device_add(dev2)
> mutex_unlock(&gdp_mutex);
> ->get_device_parent()
> ->kobject_del()
> mutex_lock(&gdp_mutex)
> kobj_kset_leave(kobj); -->del "fw1.bin" kobj in kset
> list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
> kobject_put(kobj->parent); /* No lock :)*/
> if (k->parent == parent_kobj) {
>
> ->kref_put() --> firmware ref ->0
> kobj = kobject_get(k); -> k is "firmware"
> dir
> ->kboject_release()
> break;
>
> ->kobject_del()
> }
>
> /*here deletes firmware entry in kset*/
> mutex_unlock(&gdp_mutex)
>
> ->dev2->kobj.parent = kobj -> kobj is released already
Sorry, I can't understand the above because it is shown as
mess in my email editor.
>
>
>
> PATH 1 is started removing the kobject of "fw1.bin" and its parent
> "firmware"
> .
> cleanup_device_parent(dev1) makes firmware ref count to 1, by calling
> kobject_put(firmware) with gdp_mutex held.
>
> and kobject_del(dev1->kobj) will again calls kobject_put(kobj->parent)
> without holding gdp_mutex.
>
> In PATH2, glue_dir is able to find "firmware" kobj, as firmware dir kobj is
> deleted from the glue_dir list at kboject_release().
The glue_dir can't be found after it is deleted from the other path, can it?
The gdp_mutex is used to avoid the race. If glue_dir isn't deleted, it will
be get with increasing the refer counter, so it won't be freed from another
path. If glue_dir is deleted from aother path, current path can't found
in get_device_parent() at all, so a new glue_dir will be created and added.
So I still don't see your race, maybe I am wrong?
> and it calls kobject_get(firmware), by the time PATH1 calls
> kobject_release(firmware).
>
> So PATH2 got reference of freed firmware kobj and added as parent to
> "fw2.bin" kobj.
>
> I think, here is possible fix for this race:
>
> ------------------------8<-------------------------------------
> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 5d8b713..47bc082 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1224,7 +1224,13 @@ void device_del(struct device *dev)
> BUS_NOTIFY_REMOVED_DEVICE,
> dev);
> kobject_uevent(&dev->kobj, KOBJ_REMOVE);
> cleanup_device_parent(dev);
> - kobject_del(&dev->kobj);
> +
> + if (dev->kobj.parent->kset == &dev->class->p->glue_dirs) {
> + mutex_lock(&gdp_mutex);
> + kobject_del(&dev->kobj);
> + mutex_unlock(&gdp_mutex);
> + } else
> + kobject_del(&dev->kobj);
> put_device(parent);
> }
> EXPORT_SYMBOL_GPL(device_del);
>
> --------------------------->8-----------------------------------
>
>
>>>
>>>>
>>>> [21147.455038] ------------[ cut here ]------------
>>>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
>>>> kobject_get+0x50/0x68()
>>>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>> qcrypto_module(O)
>>>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
>>>> [21147.481296] Call trace:
>>>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
>>>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
>>>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
>>>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
>>>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
>>>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
>>>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
>>>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
>>>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>> [21147.481490] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
>>>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>>>>
>>>> [21147.486436] Unable to handle kernel paging request at virtual address
>>>> 0x6b6b6b6b6b6b6bcb
>>>> [21147.493816] pgd = ffffffc0a982d000
>>>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
>>>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>>>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>> qcrypto_module(O)
>>>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
>>>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
>>>> ffffffc007880000
>>>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
>>>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
>>>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>]
>>>> pstate:
>>>> 80000145
>>>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
>>>> 0xffffffc007880058)
>>>> [21148.003673] Call trace:
>>>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
>>>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
>>>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
>>>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
>>>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>> [21148.044822] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
>>>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
>>>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>>>>
>>>> Below is the callstack where the parent is freed from the slub_debug
>>>> info.
>>>> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
>>>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
>>>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
>>>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
>>>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
>>>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
>>>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
>>>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
>>>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
>>>> 0xFFFFFFC00061C524 \\vmlinux\firmware_class\_request_firmware\out+0x71C
>>>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
>>>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
>>>> 0xFFFFFFC00061C65C
>>>> \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
>>>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
>>>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
>>>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
>>>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>>>>
>>>> For similar type of issue, I see there is an existing fix: "sysfs:
>>>> driver
>>>> core: Fix glue dir race condition by gdp_mutex".
>>>>
>>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>>>>
>>>> Still I am able to reproduce the issue. I have verified this race on
>>>> kernels: 3.10, 3.18 and 4.4.
>>>>
>>>> I followed below procedure to reproduce the issue:
>>>> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
>>>> 2. Use test_firmware, modified the test for async calls
>>>> 3. Replace WARN_ON with BUG_ON in kref_get().
>>>> I ran below script from shell:
>>>> count=0
>>>> while [ 1 ]
>>>> do
>>>> echo 3 >
>>>> /sys/devices/virtual/misc/test_firmware/trigger_ufw
>>>> if [ $? -ne 0 ]; then
>>>> print "Exiting.. "
>>>> exit 1
>>>> fi
>>>> count=$(($count +1))
>>>> echo "count $count"
>>>> done
>>>>
>>>> With below patch, I could reproduce the issue in the 2nd iteration.
>>>
>>>
>>> I will run your test script to see if there is new findings.
>>>
>>>>
>>>>
>>>> -------------------------8<----------------------------------------------
>>>>
>>>> To reproduce the race condition, use firmware test and
>>>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
>>>> releases. So that we can catch the bug easily.
>>>>
>>>> Enabled below flags in kernel config file:
>>>>
>>>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
>>>> +CONFIG_TEST_FIRMWARE=y
>>>
>>>
>>> Looks I can't reproduce the issue with your approach.
>>>
>>>>
>>>>
>>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
>>>> index 484604d..727fb24 100644
>>>> --- a/include/linux/kref.h
>>>> +++ b/include/linux/kref.h
>>>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
>>>> * condition when this kref is freeing by some other thread right
>>>> now.
>>>> * In this case one should use kref_get_unless_zero()
>>>> */
>>>> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
>>>> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
>>>> }
>>>>
>>>> /**
>>>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>>>> old mode 100644
>>>> new mode 100755
>>>> index 86374c1..14c9598
>>>> --- a/lib/test_firmware.c
>>>> +++ b/lib/test_firmware.c
>>>> @@ -18,6 +18,7 @@
>>>> #include <linux/miscdevice.h>
>>>> #include <linux/slab.h>
>>>> #include <linux/uaccess.h>
>>>> +#include <linux/async.h>
>>>>
>>>> +
>>>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
>>>> +
>>>> +static void __async_ufw_work(void *name,
>>>> + async_cookie_t cookie)
>>>> +{
>>>> + const struct firmware *fw;
>>>> + const char *fw_name = name;
>>>> + int ret;
>>>> +
>>>> + pr_err("requesting %s\n", fw_name);
>>>> +
>>>> + ret = request_firmware(&fw, fw_name, NULL);
>>>> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
>>>> + if (!ret)
>>>> + kfree(fw);
>>>> +
>>>> +}
>>>> +
>>>> +static char *name[] = { "fw1.bin", "fw2.bin"};
>>>> +
>>>> +static ssize_t trigger_ufw_store(struct device *dev,
>>>> + struct device_attribute *attr,
>>>> + const char *buf, size_t count)
>>>> +{
>>>> + int rc, i, c=0;
>>>> + u32 start;
>>>> + char *fw_name;
>>>> +
>>>> + rc = kstrtou32(buf, 0, &start);
>>>> + if (rc){
>>>> + pr_err("Invalid option\n");
>>>> + return rc;
>>>> + }
>>>> + pr_err(" no of iterations %d\n", start);
>>>> +
>>>> + for (i=0; i< start; i++)
>>>> + {
>>>> + if (c >= 2)
>>>> + c = 0;
>>>> + fw_name = name[c++];
>>>> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
>>>> &ufw_domain);
>>>> + }
>>>> + async_synchronize_full_domain(&ufw_domain);
>>>> + return count;
>>>> +}
>>>>
>>>> static DEVICE_ATTR_WO(trigger_request);
>>>> +static DEVICE_ATTR_WO(trigger_ufw);
>>>>
>>>> static int __init test_firmware_init(void)
>>>> {
>>>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
>>>> goto dereg;
>>>> }
>>>>
>>>> + rc = device_create_file(test_fw_misc_device.this_device,
>>>> + &dev_attr_trigger_ufw);
>>>> + if (rc) {
>>>> + pr_err("could not create sysfs interface: %d\n", rc);
>>>> + goto dereg;
>>>> + }
>>>> pr_warn("interface ready\n");
>>>>
>>>> return 0;
>>>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
>>>> {
>>>> release_firmware(test_firmware);
>>>> device_remove_file(test_fw_misc_device.this_device,
>>>> - &dev_attr_trigger_request);
>>>> + &dev_attr_trigger_request);
>>>> + device_remove_file(test_fw_misc_device.this_device,
>>>> + &dev_attr_trigger_ufw);
>>>> misc_deregister(&test_fw_misc_device);
>>>> pr_warn("removed interface\n");
>>>> }
>>>>
>>>>
>>>> ----------------------------8<--------------------------------------------
>>>>
>>>> Thanks and regards,
>>>> Chandrasekhar L.
>>>> --
>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>> member of
>>>> Code Aurora Forum,
>>>> a Linux Foundation Collaborative Project.
[toc] | [prev] | [next] | [standalone]
| From | Ming Lei <ming.lei@canonical.com> |
|---|---|
| Date | 2016-03-16 09:50 +0100 |
| Message-ID | <rdfjs-6uw-1@gated-at.bofh.it> |
| In reply to | #1358563 |
On Wed, Mar 16, 2016 at 3:02 PM, Chandra Sekhar Lingutla
<clingutla@codeaurora.org> wrote:
> Hi Ming,
>
>
> On 03/16/2016 07:36 AM, Ming Lei wrote:
>>
>> On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@canonical.com> wrote:
>>>
>>> Hi,
>>>
>>> On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
>>>>
>>>> Hello,
>>>>
>>>> I see possible race in _request_firmware_load function, on which I
>>>> wanted to
>>>> take your opinion.
>>>>
>>>> When system is going to low power mode, device_cache_fw_images() is
>>>> called
>>>> from pm notifier which schedules asynchronous workers to cache devices
>>>> firmware.
>>>> If more than 2 async requests falls under user helper mode, then there
>>>> is a
>>>> use after free of "firmware" directory kobject.
>>>
>>>
>>> If two requests are for getting same firmware image, only one can be sent
>>> out and be completed with user helper, please see
>>> fw_lookup_and_allocate_buf(),
>>> so the race shouldn't have been triggered in this case.
>>>
>>> So I guess your test must be involved with at least two different
>>> requests.
>>>
>>>>
>>>> The race will hit, when one asynchronous worker calls device_del() while
>>>> other asynchronous worker calls get_device_parent() in
>>>> _request_firmware_load().
>>>> After loading firmware, first worker calls device_del(), and "firmware"
>>>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put() with
>>>> gdp_mutex lock held.
>>>> Meanwhile, second async worker calls device_add(), and
>>>> get_device_parent()
>>>> is still able to find the firmware directory kobject in ksets after
>>>> getting
>>>> gdp_mutex.
>>>> This kobject gets added as parent to the second device kobject.
>>>> By the time of accessing the parent kobject, its ref count was 0 and
>>>> prints
>>>> below warning stack followed by crash.
>>>
>>>
>>> The trick here is just that we don't use 'struct device' in
>>> device_cache_fw_images(),
>>> then the firmware device's parent is null during calling device_add()
>>> from
>>> _request_firmware_load(), but this should be allowed by driver core.
>>>
>>> From firmware class view, both device_add()/device_del() is run with
>>> pair,
>>> and driver core still complains during get_device_parent(), so something
>>> inside driver core should be be wrong, IMO.
>>
>>
>> Thinking about the issue further, I believe it is a false positive which
>> is
>> caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
>>
>> 1) device_add() path
>>
>> get_device_parent()
>> ......
>> mutex_lock(&gdp_mutex);
>>
>> /* find our class-directory at the parent and reference
>> it */
>> spin_lock(&dev->class->p->glue_dirs.list_lock);
>> list_for_each_entry(k, &dev->class->p->glue_dirs.list,
>> entry)
>> if (k->parent == parent_kobj) {
>> kobj = kobject_get(k);
>> break;
>> }
>> spin_unlock(&dev->class->p->glue_dirs.list_lock);
>> if (kobj) {
>> mutex_unlock(&gdp_mutex);
>> return kobj;
>> }
>> k = class_dir_create_and_add(dev->class, parent_kobj);
>> mutex_unlock(&gdp_mutex);
>> ......
>>
>> 2) device_del() path
>>
>> cleanup_device_parent()
>> ->cleanup_glue_dir()
>> ->mutex_lock(&gdp_mutex);
>> ->kobject_put(glue_dir);
>> ->kobject_cleanup()
>> ->kobject_del()
>> ->kobj_kset_leave()
>> ->mutex_unlock(&gdp_mutex);
>>
>> So gdp_mutex is held wrt. both looking up/adding the parent kobject
>> and removing the parent kobject. Actually with this lock, both glur_dir
>> kobject's referece counting and joining/leaving kset are run atomically.
>>
>> The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
>> which causes kobject_cleanup() to be run in workqueue context and the
>> lock of gdp_mutex can't be hold in that situation anymore. That is the
>> root
>> cause for your race.
>>
>> That also said DEBUG_KOBJECT_RELEASE might cause trouble in
>> some situations.
>>
>> Thanks,
>> Ming
>>
> I agree that, CONFIG_DEBUG_KOBJECT_RELEASE can cause the race, as it delays
> call to kobject_cleanup() which deletes kobj entry in glue_dir list.
>
> I see the race even after disabling CONFIG_DEBUG_KOBJECT_RELEASE.
>
> The race is between kobject_put() and kobject_get() for the "firmware"
> directory.
>
> In device_del() path, I see the race after the call of
> cleanup_device_parent().
> cleanup_device_parent() calls kobject_put(glue_dir) with gdp_mutex lock
> holding,
> So ideally, to call kobject_put/kobject_get(glue_dir) we need to acquire
> gdp_mutex.
>
> but kobject_del(kobj) will not hold the gdp_mutex lock while calling
> kobject_put(kobj->parent).
>
> Here is the race:
>
> Consider 2 async works calls request_firmware() for 2 different binaries
> (fw1.bin, fw2.bin)
> Async work1 got scheduled first, and it falls in user helper mode so it
> creates "firmware" dir
> and then creates "fw1.bin" directory to load data from user.
> After load completion or timeout, it starts cleanup dir's, meantime async
> work2 got scheduled and
> it also falls in user helper mode, and story starts here:
>
> PATH1 req fw for "fw1.bin" PATH2
> req fw for "fw2.bin"
> _request_firmware_load()
> device_del(dev1)
>
> ->cleanup_device_parent()
>
> mutex_lock(&gdp_mutex);
> _request_firmware_load("fw2.bin")
> kobject_put(kobj->parent); --> firmware ref ->1
> ->device_add(dev2)
> mutex_unlock(&gdp_mutex);
> ->get_device_parent()
> ->kobject_del()
> mutex_lock(&gdp_mutex)
> kobj_kset_leave(kobj); -->del "fw1.bin" kobj in kset
> list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
> kobject_put(kobj->parent); /* No lock :)*/
> if (k->parent == parent_kobj) {
>
> ->kref_put() --> firmware ref ->0
> kobj = kobject_get(k); -> k is "firmware"
> dir
> ->kboject_release()
> break;
>
> ->kobject_del()
> }
>
> /*here deletes firmware entry in kset*/
> mutex_unlock(&gdp_mutex)
>
> ->dev2->kobj.parent = kobj -> kobj is released already
>
>
>
> PATH 1 is started removing the kobject of "fw1.bin" and its parent
> "firmware"
> .
> cleanup_device_parent(dev1) makes firmware ref count to 1, by calling
> kobject_put(firmware) with gdp_mutex held.
>
> and kobject_del(dev1->kobj) will again calls kobject_put(kobj->parent)
> without holding gdp_mutex.
>
> In PATH2, glue_dir is able to find "firmware" kobj, as firmware dir kobj is
> deleted from the glue_dir list at kboject_release().
> and it calls kobject_get(firmware), by the time PATH1 calls
> kobject_release(firmware).
>
> So PATH2 got reference of freed firmware kobj and added as parent to
> "fw2.bin" kobj.
>
> I think, here is possible fix for this race:
>
> ------------------------8<-------------------------------------
> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 5d8b713..47bc082 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1224,7 +1224,13 @@ void device_del(struct device *dev)
> BUS_NOTIFY_REMOVED_DEVICE,
> dev);
> kobject_uevent(&dev->kobj, KOBJ_REMOVE);
> cleanup_device_parent(dev);
> - kobject_del(&dev->kobj);
> +
> + if (dev->kobj.parent->kset == &dev->class->p->glue_dirs) {
> + mutex_lock(&gdp_mutex);
> + kobject_del(&dev->kobj);
> + mutex_unlock(&gdp_mutex);
> + } else
> + kobject_del(&dev->kobj);
> put_device(parent);
> }
> EXPORT_SYMBOL_GPL(device_del);
>
> --------------------------->8-----------------------------------
OK, one simpler way is to move cleanup_device_parent(dev)
after kobject_del(&dev->kobj), which looks more clean too.
>
>
>>>
>>>>
>>>> [21147.455038] ------------[ cut here ]------------
>>>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
>>>> kobject_get+0x50/0x68()
>>>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>> qcrypto_module(O)
>>>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
>>>> [21147.481296] Call trace:
>>>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
>>>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
>>>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
>>>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
>>>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
>>>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
>>>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
>>>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
>>>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>> [21147.481490] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
>>>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>>>>
>>>> [21147.486436] Unable to handle kernel paging request at virtual address
>>>> 0x6b6b6b6b6b6b6bcb
>>>> [21147.493816] pgd = ffffffc0a982d000
>>>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
>>>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>>>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>> qcrypto_module(O)
>>>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
>>>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
>>>> ffffffc007880000
>>>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
>>>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
>>>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>]
>>>> pstate:
>>>> 80000145
>>>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
>>>> 0xffffffc007880058)
>>>> [21148.003673] Call trace:
>>>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
>>>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
>>>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
>>>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
>>>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>> [21148.044822] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
>>>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
>>>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>>>>
>>>> Below is the callstack where the parent is freed from the slub_debug
>>>> info.
>>>> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
>>>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
>>>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
>>>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
>>>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
>>>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
>>>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
>>>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
>>>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
>>>> 0xFFFFFFC00061C524 \\vmlinux\firmware_class\_request_firmware\out+0x71C
>>>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
>>>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
>>>> 0xFFFFFFC00061C65C
>>>> \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
>>>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
>>>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
>>>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
>>>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>>>>
>>>> For similar type of issue, I see there is an existing fix: "sysfs:
>>>> driver
>>>> core: Fix glue dir race condition by gdp_mutex".
>>>>
>>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>>>>
>>>> Still I am able to reproduce the issue. I have verified this race on
>>>> kernels: 3.10, 3.18 and 4.4.
>>>>
>>>> I followed below procedure to reproduce the issue:
>>>> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
>>>> 2. Use test_firmware, modified the test for async calls
>>>> 3. Replace WARN_ON with BUG_ON in kref_get().
>>>> I ran below script from shell:
>>>> count=0
>>>> while [ 1 ]
>>>> do
>>>> echo 3 >
>>>> /sys/devices/virtual/misc/test_firmware/trigger_ufw
>>>> if [ $? -ne 0 ]; then
>>>> print "Exiting.. "
>>>> exit 1
>>>> fi
>>>> count=$(($count +1))
>>>> echo "count $count"
>>>> done
>>>>
>>>> With below patch, I could reproduce the issue in the 2nd iteration.
>>>
>>>
>>> I will run your test script to see if there is new findings.
>>>
>>>>
>>>>
>>>> -------------------------8<----------------------------------------------
>>>>
>>>> To reproduce the race condition, use firmware test and
>>>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
>>>> releases. So that we can catch the bug easily.
>>>>
>>>> Enabled below flags in kernel config file:
>>>>
>>>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
>>>> +CONFIG_TEST_FIRMWARE=y
>>>
>>>
>>> Looks I can't reproduce the issue with your approach.
>>>
>>>>
>>>>
>>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
>>>> index 484604d..727fb24 100644
>>>> --- a/include/linux/kref.h
>>>> +++ b/include/linux/kref.h
>>>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
>>>> * condition when this kref is freeing by some other thread right
>>>> now.
>>>> * In this case one should use kref_get_unless_zero()
>>>> */
>>>> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
>>>> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
>>>> }
>>>>
>>>> /**
>>>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>>>> old mode 100644
>>>> new mode 100755
>>>> index 86374c1..14c9598
>>>> --- a/lib/test_firmware.c
>>>> +++ b/lib/test_firmware.c
>>>> @@ -18,6 +18,7 @@
>>>> #include <linux/miscdevice.h>
>>>> #include <linux/slab.h>
>>>> #include <linux/uaccess.h>
>>>> +#include <linux/async.h>
>>>>
>>>> +
>>>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
>>>> +
>>>> +static void __async_ufw_work(void *name,
>>>> + async_cookie_t cookie)
>>>> +{
>>>> + const struct firmware *fw;
>>>> + const char *fw_name = name;
>>>> + int ret;
>>>> +
>>>> + pr_err("requesting %s\n", fw_name);
>>>> +
>>>> + ret = request_firmware(&fw, fw_name, NULL);
>>>> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
>>>> + if (!ret)
>>>> + kfree(fw);
>>>> +
>>>> +}
>>>> +
>>>> +static char *name[] = { "fw1.bin", "fw2.bin"};
>>>> +
>>>> +static ssize_t trigger_ufw_store(struct device *dev,
>>>> + struct device_attribute *attr,
>>>> + const char *buf, size_t count)
>>>> +{
>>>> + int rc, i, c=0;
>>>> + u32 start;
>>>> + char *fw_name;
>>>> +
>>>> + rc = kstrtou32(buf, 0, &start);
>>>> + if (rc){
>>>> + pr_err("Invalid option\n");
>>>> + return rc;
>>>> + }
>>>> + pr_err(" no of iterations %d\n", start);
>>>> +
>>>> + for (i=0; i< start; i++)
>>>> + {
>>>> + if (c >= 2)
>>>> + c = 0;
>>>> + fw_name = name[c++];
>>>> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
>>>> &ufw_domain);
>>>> + }
>>>> + async_synchronize_full_domain(&ufw_domain);
>>>> + return count;
>>>> +}
>>>>
>>>> static DEVICE_ATTR_WO(trigger_request);
>>>> +static DEVICE_ATTR_WO(trigger_ufw);
>>>>
>>>> static int __init test_firmware_init(void)
>>>> {
>>>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
>>>> goto dereg;
>>>> }
>>>>
>>>> + rc = device_create_file(test_fw_misc_device.this_device,
>>>> + &dev_attr_trigger_ufw);
>>>> + if (rc) {
>>>> + pr_err("could not create sysfs interface: %d\n", rc);
>>>> + goto dereg;
>>>> + }
>>>> pr_warn("interface ready\n");
>>>>
>>>> return 0;
>>>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
>>>> {
>>>> release_firmware(test_firmware);
>>>> device_remove_file(test_fw_misc_device.this_device,
>>>> - &dev_attr_trigger_request);
>>>> + &dev_attr_trigger_request);
>>>> + device_remove_file(test_fw_misc_device.this_device,
>>>> + &dev_attr_trigger_ufw);
>>>> misc_deregister(&test_fw_misc_device);
>>>> pr_warn("removed interface\n");
>>>> }
>>>>
>>>>
>>>> ----------------------------8<--------------------------------------------
>>>>
>>>> Thanks and regards,
>>>> Chandrasekhar L.
>>>> --
>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>> member of
>>>> Code Aurora Forum,
>>>> a Linux Foundation Collaborative Project.
[toc] | [prev] | [next] | [standalone]
| From | Chandra Sekhar Lingutla <clingutla@codeaurora.org> |
|---|---|
| Date | 2016-03-16 09:50 +0100 |
| Message-ID | <rdfjs-6uw-5@gated-at.bofh.it> |
| In reply to | #1358721 |
On 03/16/2016 02:12 PM, Ming Lei wrote:
> On Wed, Mar 16, 2016 at 3:02 PM, Chandra Sekhar Lingutla
> <clingutla@codeaurora.org> wrote:
>> Hi Ming,
>>
>>
>> On 03/16/2016 07:36 AM, Ming Lei wrote:
>>>
>>> On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@canonical.com> wrote:
>>>>
>>>> Hi,
>>>>
>>>> On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
>>>>>
>>>>> Hello,
>>>>>
>>>>> I see possible race in _request_firmware_load function, on which I
>>>>> wanted to
>>>>> take your opinion.
>>>>>
>>>>> When system is going to low power mode, device_cache_fw_images() is
>>>>> called
>>>>> from pm notifier which schedules asynchronous workers to cache devices
>>>>> firmware.
>>>>> If more than 2 async requests falls under user helper mode, then there
>>>>> is a
>>>>> use after free of "firmware" directory kobject.
>>>>
>>>>
>>>> If two requests are for getting same firmware image, only one can be sent
>>>> out and be completed with user helper, please see
>>>> fw_lookup_and_allocate_buf(),
>>>> so the race shouldn't have been triggered in this case.
>>>>
>>>> So I guess your test must be involved with at least two different
>>>> requests.
>>>>
>>>>>
>>>>> The race will hit, when one asynchronous worker calls device_del() while
>>>>> other asynchronous worker calls get_device_parent() in
>>>>> _request_firmware_load().
>>>>> After loading firmware, first worker calls device_del(), and "firmware"
>>>>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put() with
>>>>> gdp_mutex lock held.
>>>>> Meanwhile, second async worker calls device_add(), and
>>>>> get_device_parent()
>>>>> is still able to find the firmware directory kobject in ksets after
>>>>> getting
>>>>> gdp_mutex.
>>>>> This kobject gets added as parent to the second device kobject.
>>>>> By the time of accessing the parent kobject, its ref count was 0 and
>>>>> prints
>>>>> below warning stack followed by crash.
>>>>
>>>>
>>>> The trick here is just that we don't use 'struct device' in
>>>> device_cache_fw_images(),
>>>> then the firmware device's parent is null during calling device_add()
>>>> from
>>>> _request_firmware_load(), but this should be allowed by driver core.
>>>>
>>>> From firmware class view, both device_add()/device_del() is run with
>>>> pair,
>>>> and driver core still complains during get_device_parent(), so something
>>>> inside driver core should be be wrong, IMO.
>>>
>>>
>>> Thinking about the issue further, I believe it is a false positive which
>>> is
>>> caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
>>>
>>> 1) device_add() path
>>>
>>> get_device_parent()
>>> ......
>>> mutex_lock(&gdp_mutex);
>>>
>>> /* find our class-directory at the parent and reference
>>> it */
>>> spin_lock(&dev->class->p->glue_dirs.list_lock);
>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list,
>>> entry)
>>> if (k->parent == parent_kobj) {
>>> kobj = kobject_get(k);
>>> break;
>>> }
>>> spin_unlock(&dev->class->p->glue_dirs.list_lock);
>>> if (kobj) {
>>> mutex_unlock(&gdp_mutex);
>>> return kobj;
>>> }
>>> k = class_dir_create_and_add(dev->class, parent_kobj);
>>> mutex_unlock(&gdp_mutex);
>>> ......
>>>
>>> 2) device_del() path
>>>
>>> cleanup_device_parent()
>>> ->cleanup_glue_dir()
>>> ->mutex_lock(&gdp_mutex);
>>> ->kobject_put(glue_dir);
>>> ->kobject_cleanup()
>>> ->kobject_del()
>>> ->kobj_kset_leave()
>>> ->mutex_unlock(&gdp_mutex);
>>>
>>> So gdp_mutex is held wrt. both looking up/adding the parent kobject
>>> and removing the parent kobject. Actually with this lock, both glur_dir
>>> kobject's referece counting and joining/leaving kset are run atomically.
>>>
>>> The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
>>> which causes kobject_cleanup() to be run in workqueue context and the
>>> lock of gdp_mutex can't be hold in that situation anymore. That is the
>>> root
>>> cause for your race.
>>>
>>> That also said DEBUG_KOBJECT_RELEASE might cause trouble in
>>> some situations.
>>>
>>> Thanks,
>>> Ming
>>>
>> I agree that, CONFIG_DEBUG_KOBJECT_RELEASE can cause the race, as it delays
>> call to kobject_cleanup() which deletes kobj entry in glue_dir list.
>>
>> I see the race even after disabling CONFIG_DEBUG_KOBJECT_RELEASE.
>>
>> The race is between kobject_put() and kobject_get() for the "firmware"
>> directory.
>>
>> In device_del() path, I see the race after the call of
>> cleanup_device_parent().
>> cleanup_device_parent() calls kobject_put(glue_dir) with gdp_mutex lock
>> holding,
>> So ideally, to call kobject_put/kobject_get(glue_dir) we need to acquire
>> gdp_mutex.
>>
>> but kobject_del(kobj) will not hold the gdp_mutex lock while calling
>> kobject_put(kobj->parent).
>>
>> Here is the race:
>>
>> Consider 2 async works calls request_firmware() for 2 different binaries
>> (fw1.bin, fw2.bin)
>> Async work1 got scheduled first, and it falls in user helper mode so it
>> creates "firmware" dir
>> and then creates "fw1.bin" directory to load data from user.
>> After load completion or timeout, it starts cleanup dir's, meantime async
>> work2 got scheduled and
>> it also falls in user helper mode, and story starts here:
>>
>> PATH1 req fw for "fw1.bin" PATH2
>> req fw for "fw2.bin"
>> _request_firmware_load()
>> device_del(dev1)
>>
>> ->cleanup_device_parent()
>>
>> mutex_lock(&gdp_mutex);
>> _request_firmware_load("fw2.bin")
>> kobject_put(kobj->parent); --> firmware ref ->1
>> ->device_add(dev2)
>> mutex_unlock(&gdp_mutex);
>> ->get_device_parent()
>> ->kobject_del()
>> mutex_lock(&gdp_mutex)
>> kobj_kset_leave(kobj); -->del "fw1.bin" kobj in kset
>> list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
>> kobject_put(kobj->parent); /* No lock :)*/
>> if (k->parent == parent_kobj) {
>>
>> ->kref_put() --> firmware ref ->0
>> kobj = kobject_get(k); -> k is "firmware"
>> dir
>> ->kboject_release()
>> break;
>>
>> ->kobject_del()
>> }
>>
>> /*here deletes firmware entry in kset*/
>> mutex_unlock(&gdp_mutex)
>>
>> ->dev2->kobj.parent = kobj -> kobj is released already
>>
>>
>>
>> PATH 1 is started removing the kobject of "fw1.bin" and its parent
>> "firmware"
>> .
>> cleanup_device_parent(dev1) makes firmware ref count to 1, by calling
>> kobject_put(firmware) with gdp_mutex held.
>>
>> and kobject_del(dev1->kobj) will again calls kobject_put(kobj->parent)
>> without holding gdp_mutex.
>>
>> In PATH2, glue_dir is able to find "firmware" kobj, as firmware dir kobj is
>> deleted from the glue_dir list at kboject_release().
>> and it calls kobject_get(firmware), by the time PATH1 calls
>> kobject_release(firmware).
>>
>> So PATH2 got reference of freed firmware kobj and added as parent to
>> "fw2.bin" kobj.
>>
>> I think, here is possible fix for this race:
>>
>> ------------------------8<-------------------------------------
>> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
>>
>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>> index 5d8b713..47bc082 100644
>> --- a/drivers/base/core.c
>> +++ b/drivers/base/core.c
>> @@ -1224,7 +1224,13 @@ void device_del(struct device *dev)
>> BUS_NOTIFY_REMOVED_DEVICE,
>> dev);
>> kobject_uevent(&dev->kobj, KOBJ_REMOVE);
>> cleanup_device_parent(dev);
>> - kobject_del(&dev->kobj);
>> +
>> + if (dev->kobj.parent->kset == &dev->class->p->glue_dirs) {
>> + mutex_lock(&gdp_mutex);
>> + kobject_del(&dev->kobj);
>> + mutex_unlock(&gdp_mutex);
>> + } else
>> + kobject_del(&dev->kobj);
>> put_device(parent);
>> }
>> EXPORT_SYMBOL_GPL(device_del);
>>
>> --------------------------->8-----------------------------------
>
> OK, one simpler way is to move cleanup_device_parent(dev)
> after kobject_del(&dev->kobj), which looks more clean too.
>
No, We can't move that, bcz kobject_del(&dev->kobj) will clear the parent.
>>
>>
>>>>
>>>>>
>>>>> [21147.455038] ------------[ cut here ]------------
>>>>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
>>>>> kobject_get+0x50/0x68()
>>>>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>> qcrypto_module(O)
>>>>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
>>>>> [21147.481296] Call trace:
>>>>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
>>>>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
>>>>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
>>>>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
>>>>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
>>>>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
>>>>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
>>>>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
>>>>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>> [21147.481490] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
>>>>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>>>>>
>>>>> [21147.486436] Unable to handle kernel paging request at virtual address
>>>>> 0x6b6b6b6b6b6b6bcb
>>>>> [21147.493816] pgd = ffffffc0a982d000
>>>>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
>>>>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>>>>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>> qcrypto_module(O)
>>>>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
>>>>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
>>>>> ffffffc007880000
>>>>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
>>>>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
>>>>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>]
>>>>> pstate:
>>>>> 80000145
>>>>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
>>>>> 0xffffffc007880058)
>>>>> [21148.003673] Call trace:
>>>>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
>>>>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
>>>>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
>>>>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
>>>>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>> [21148.044822] [<ffffffc00061c65c>] __async_dev_cache_fw_image+0x14/0x54
>>>>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
>>>>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>>>>>
>>>>> Below is the callstack where the parent is freed from the slub_debug
>>>>> info.
>>>>> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
>>>>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
>>>>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
>>>>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
>>>>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
>>>>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
>>>>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
>>>>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
>>>>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
>>>>> 0xFFFFFFC00061C524 \\vmlinux\firmware_class\_request_firmware\out+0x71C
>>>>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
>>>>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
>>>>> 0xFFFFFFC00061C65C
>>>>> \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
>>>>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
>>>>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
>>>>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
>>>>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>>>>>
>>>>> For similar type of issue, I see there is an existing fix: "sysfs:
>>>>> driver
>>>>> core: Fix glue dir race condition by gdp_mutex".
>>>>>
>>>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>>>>>
>>>>> Still I am able to reproduce the issue. I have verified this race on
>>>>> kernels: 3.10, 3.18 and 4.4.
>>>>>
>>>>> I followed below procedure to reproduce the issue:
>>>>> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
>>>>> 2. Use test_firmware, modified the test for async calls
>>>>> 3. Replace WARN_ON with BUG_ON in kref_get().
>>>>> I ran below script from shell:
>>>>> count=0
>>>>> while [ 1 ]
>>>>> do
>>>>> echo 3 >
>>>>> /sys/devices/virtual/misc/test_firmware/trigger_ufw
>>>>> if [ $? -ne 0 ]; then
>>>>> print "Exiting.. "
>>>>> exit 1
>>>>> fi
>>>>> count=$(($count +1))
>>>>> echo "count $count"
>>>>> done
>>>>>
>>>>> With below patch, I could reproduce the issue in the 2nd iteration.
>>>>
>>>>
>>>> I will run your test script to see if there is new findings.
>>>>
>>>>>
>>>>>
>>>>> -------------------------8<----------------------------------------------
>>>>>
>>>>> To reproduce the race condition, use firmware test and
>>>>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
>>>>> releases. So that we can catch the bug easily.
>>>>>
>>>>> Enabled below flags in kernel config file:
>>>>>
>>>>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
>>>>> +CONFIG_TEST_FIRMWARE=y
>>>>
>>>>
>>>> Looks I can't reproduce the issue with your approach.
>>>>
>>>>>
>>>>>
>>>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
>>>>> index 484604d..727fb24 100644
>>>>> --- a/include/linux/kref.h
>>>>> +++ b/include/linux/kref.h
>>>>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
>>>>> * condition when this kref is freeing by some other thread right
>>>>> now.
>>>>> * In this case one should use kref_get_unless_zero()
>>>>> */
>>>>> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
>>>>> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
>>>>> }
>>>>>
>>>>> /**
>>>>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>>>>> old mode 100644
>>>>> new mode 100755
>>>>> index 86374c1..14c9598
>>>>> --- a/lib/test_firmware.c
>>>>> +++ b/lib/test_firmware.c
>>>>> @@ -18,6 +18,7 @@
>>>>> #include <linux/miscdevice.h>
>>>>> #include <linux/slab.h>
>>>>> #include <linux/uaccess.h>
>>>>> +#include <linux/async.h>
>>>>>
>>>>> +
>>>>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
>>>>> +
>>>>> +static void __async_ufw_work(void *name,
>>>>> + async_cookie_t cookie)
>>>>> +{
>>>>> + const struct firmware *fw;
>>>>> + const char *fw_name = name;
>>>>> + int ret;
>>>>> +
>>>>> + pr_err("requesting %s\n", fw_name);
>>>>> +
>>>>> + ret = request_firmware(&fw, fw_name, NULL);
>>>>> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
>>>>> + if (!ret)
>>>>> + kfree(fw);
>>>>> +
>>>>> +}
>>>>> +
>>>>> +static char *name[] = { "fw1.bin", "fw2.bin"};
>>>>> +
>>>>> +static ssize_t trigger_ufw_store(struct device *dev,
>>>>> + struct device_attribute *attr,
>>>>> + const char *buf, size_t count)
>>>>> +{
>>>>> + int rc, i, c=0;
>>>>> + u32 start;
>>>>> + char *fw_name;
>>>>> +
>>>>> + rc = kstrtou32(buf, 0, &start);
>>>>> + if (rc){
>>>>> + pr_err("Invalid option\n");
>>>>> + return rc;
>>>>> + }
>>>>> + pr_err(" no of iterations %d\n", start);
>>>>> +
>>>>> + for (i=0; i< start; i++)
>>>>> + {
>>>>> + if (c >= 2)
>>>>> + c = 0;
>>>>> + fw_name = name[c++];
>>>>> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
>>>>> &ufw_domain);
>>>>> + }
>>>>> + async_synchronize_full_domain(&ufw_domain);
>>>>> + return count;
>>>>> +}
>>>>>
>>>>> static DEVICE_ATTR_WO(trigger_request);
>>>>> +static DEVICE_ATTR_WO(trigger_ufw);
>>>>>
>>>>> static int __init test_firmware_init(void)
>>>>> {
>>>>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
>>>>> goto dereg;
>>>>> }
>>>>>
>>>>> + rc = device_create_file(test_fw_misc_device.this_device,
>>>>> + &dev_attr_trigger_ufw);
>>>>> + if (rc) {
>>>>> + pr_err("could not create sysfs interface: %d\n", rc);
>>>>> + goto dereg;
>>>>> + }
>>>>> pr_warn("interface ready\n");
>>>>>
>>>>> return 0;
>>>>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
>>>>> {
>>>>> release_firmware(test_firmware);
>>>>> device_remove_file(test_fw_misc_device.this_device,
>>>>> - &dev_attr_trigger_request);
>>>>> + &dev_attr_trigger_request);
>>>>> + device_remove_file(test_fw_misc_device.this_device,
>>>>> + &dev_attr_trigger_ufw);
>>>>> misc_deregister(&test_fw_misc_device);
>>>>> pr_warn("removed interface\n");
>>>>> }
>>>>>
>>>>>
>>>>> ----------------------------8<--------------------------------------------
>>>>>
>>>>> Thanks and regards,
>>>>> Chandrasekhar L.
>>>>> --
>>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>>> member of
>>>>> Code Aurora Forum,
>>>>> a Linux Foundation Collaborative Project.
[toc] | [prev] | [next] | [standalone]
| From | Ming Lei <ming.lei@canonical.com> |
|---|---|
| Date | 2016-03-16 10:00 +0100 |
| Message-ID | <rdft9-6zO-29@gated-at.bofh.it> |
| In reply to | #1358723 |
On Wed, Mar 16, 2016 at 4:48 PM, Chandra Sekhar Lingutla
<clingutla@codeaurora.org> wrote:
> On 03/16/2016 02:12 PM, Ming Lei wrote:
>>
>> On Wed, Mar 16, 2016 at 3:02 PM, Chandra Sekhar Lingutla
>> <clingutla@codeaurora.org> wrote:
>>>
>>> Hi Ming,
>>>
>>>
>>> On 03/16/2016 07:36 AM, Ming Lei wrote:
>>>>
>>>>
>>>> On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@canonical.com>
>>>> wrote:
>>>>>
>>>>>
>>>>> Hi,
>>>>>
>>>>> On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
>>>>>>
>>>>>>
>>>>>> Hello,
>>>>>>
>>>>>> I see possible race in _request_firmware_load function, on which I
>>>>>> wanted to
>>>>>> take your opinion.
>>>>>>
>>>>>> When system is going to low power mode, device_cache_fw_images() is
>>>>>> called
>>>>>> from pm notifier which schedules asynchronous workers to cache devices
>>>>>> firmware.
>>>>>> If more than 2 async requests falls under user helper mode, then there
>>>>>> is a
>>>>>> use after free of "firmware" directory kobject.
>>>>>
>>>>>
>>>>>
>>>>> If two requests are for getting same firmware image, only one can be
>>>>> sent
>>>>> out and be completed with user helper, please see
>>>>> fw_lookup_and_allocate_buf(),
>>>>> so the race shouldn't have been triggered in this case.
>>>>>
>>>>> So I guess your test must be involved with at least two different
>>>>> requests.
>>>>>
>>>>>>
>>>>>> The race will hit, when one asynchronous worker calls device_del()
>>>>>> while
>>>>>> other asynchronous worker calls get_device_parent() in
>>>>>> _request_firmware_load().
>>>>>> After loading firmware, first worker calls device_del(), and
>>>>>> "firmware"
>>>>>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put()
>>>>>> with
>>>>>> gdp_mutex lock held.
>>>>>> Meanwhile, second async worker calls device_add(), and
>>>>>> get_device_parent()
>>>>>> is still able to find the firmware directory kobject in ksets after
>>>>>> getting
>>>>>> gdp_mutex.
>>>>>> This kobject gets added as parent to the second device kobject.
>>>>>> By the time of accessing the parent kobject, its ref count was 0 and
>>>>>> prints
>>>>>> below warning stack followed by crash.
>>>>>
>>>>>
>>>>>
>>>>> The trick here is just that we don't use 'struct device' in
>>>>> device_cache_fw_images(),
>>>>> then the firmware device's parent is null during calling device_add()
>>>>> from
>>>>> _request_firmware_load(), but this should be allowed by driver core.
>>>>>
>>>>> From firmware class view, both device_add()/device_del() is run with
>>>>> pair,
>>>>> and driver core still complains during get_device_parent(), so
>>>>> something
>>>>> inside driver core should be be wrong, IMO.
>>>>
>>>>
>>>>
>>>> Thinking about the issue further, I believe it is a false positive which
>>>> is
>>>> caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
>>>>
>>>> 1) device_add() path
>>>>
>>>> get_device_parent()
>>>> ......
>>>> mutex_lock(&gdp_mutex);
>>>>
>>>> /* find our class-directory at the parent and
>>>> reference
>>>> it */
>>>> spin_lock(&dev->class->p->glue_dirs.list_lock);
>>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list,
>>>> entry)
>>>> if (k->parent == parent_kobj) {
>>>> kobj = kobject_get(k);
>>>> break;
>>>> }
>>>> spin_unlock(&dev->class->p->glue_dirs.list_lock);
>>>> if (kobj) {
>>>> mutex_unlock(&gdp_mutex);
>>>> return kobj;
>>>> }
>>>> k = class_dir_create_and_add(dev->class, parent_kobj);
>>>> mutex_unlock(&gdp_mutex);
>>>> ......
>>>>
>>>> 2) device_del() path
>>>>
>>>> cleanup_device_parent()
>>>> ->cleanup_glue_dir()
>>>> ->mutex_lock(&gdp_mutex);
>>>> ->kobject_put(glue_dir);
>>>> ->kobject_cleanup()
>>>> ->kobject_del()
>>>> ->kobj_kset_leave()
>>>> ->mutex_unlock(&gdp_mutex);
>>>>
>>>> So gdp_mutex is held wrt. both looking up/adding the parent kobject
>>>> and removing the parent kobject. Actually with this lock, both glur_dir
>>>> kobject's referece counting and joining/leaving kset are run atomically.
>>>>
>>>> The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
>>>> which causes kobject_cleanup() to be run in workqueue context and the
>>>> lock of gdp_mutex can't be hold in that situation anymore. That is the
>>>> root
>>>> cause for your race.
>>>>
>>>> That also said DEBUG_KOBJECT_RELEASE might cause trouble in
>>>> some situations.
>>>>
>>>> Thanks,
>>>> Ming
>>>>
>>> I agree that, CONFIG_DEBUG_KOBJECT_RELEASE can cause the race, as it
>>> delays
>>> call to kobject_cleanup() which deletes kobj entry in glue_dir list.
>>>
>>> I see the race even after disabling CONFIG_DEBUG_KOBJECT_RELEASE.
>>>
>>> The race is between kobject_put() and kobject_get() for the "firmware"
>>> directory.
>>>
>>> In device_del() path, I see the race after the call of
>>> cleanup_device_parent().
>>> cleanup_device_parent() calls kobject_put(glue_dir) with gdp_mutex lock
>>> holding,
>>> So ideally, to call kobject_put/kobject_get(glue_dir) we need to acquire
>>> gdp_mutex.
>>>
>>> but kobject_del(kobj) will not hold the gdp_mutex lock while calling
>>> kobject_put(kobj->parent).
>>>
>>> Here is the race:
>>>
>>> Consider 2 async works calls request_firmware() for 2 different binaries
>>> (fw1.bin, fw2.bin)
>>> Async work1 got scheduled first, and it falls in user helper mode so it
>>> creates "firmware" dir
>>> and then creates "fw1.bin" directory to load data from user.
>>> After load completion or timeout, it starts cleanup dir's, meantime async
>>> work2 got scheduled and
>>> it also falls in user helper mode, and story starts here:
>>>
>>> PATH1 req fw for "fw1.bin"
>>> PATH2
>>> req fw for "fw2.bin"
>>> _request_firmware_load()
>>> device_del(dev1)
>>>
>>> ->cleanup_device_parent()
>>>
>>> mutex_lock(&gdp_mutex);
>>>
>>> _request_firmware_load("fw2.bin")
>>> kobject_put(kobj->parent); --> firmware ref ->1
>>> ->device_add(dev2)
>>> mutex_unlock(&gdp_mutex);
>>> ->get_device_parent()
>>> ->kobject_del()
>>> mutex_lock(&gdp_mutex)
>>> kobj_kset_leave(kobj); -->del "fw1.bin" kobj in kset
>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
>>> kobject_put(kobj->parent); /* No lock :)*/
>>> if (k->parent == parent_kobj) {
>>>
>>> ->kref_put() --> firmware ref ->0
>>> kobj = kobject_get(k); -> k is "firmware"
>>> dir
>>> ->kboject_release()
>>> break;
>>>
>>> ->kobject_del()
>>> }
>>>
>>> /*here deletes firmware entry in kset*/
>>> mutex_unlock(&gdp_mutex)
>>>
>>> ->dev2->kobj.parent = kobj -> kobj is released already
>>>
>>>
>>>
>>> PATH 1 is started removing the kobject of "fw1.bin" and its parent
>>> "firmware"
>>> .
>>> cleanup_device_parent(dev1) makes firmware ref count to 1, by calling
>>> kobject_put(firmware) with gdp_mutex held.
>>>
>>> and kobject_del(dev1->kobj) will again calls kobject_put(kobj->parent)
>>> without holding gdp_mutex.
>>>
>>> In PATH2, glue_dir is able to find "firmware" kobj, as firmware dir kobj
>>> is
>>> deleted from the glue_dir list at kboject_release().
>>> and it calls kobject_get(firmware), by the time PATH1 calls
>>> kobject_release(firmware).
>>>
>>> So PATH2 got reference of freed firmware kobj and added as parent to
>>> "fw2.bin" kobj.
>>>
>>> I think, here is possible fix for this race:
>>>
>>> ------------------------8<-------------------------------------
>>> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
>>>
>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>>> index 5d8b713..47bc082 100644
>>> --- a/drivers/base/core.c
>>> +++ b/drivers/base/core.c
>>> @@ -1224,7 +1224,13 @@ void device_del(struct device *dev)
>>> BUS_NOTIFY_REMOVED_DEVICE,
>>> dev);
>>> kobject_uevent(&dev->kobj, KOBJ_REMOVE);
>>> cleanup_device_parent(dev);
>>> - kobject_del(&dev->kobj);
>>> +
>>> + if (dev->kobj.parent->kset == &dev->class->p->glue_dirs) {
>>> + mutex_lock(&gdp_mutex);
>>> + kobject_del(&dev->kobj);
>>> + mutex_unlock(&gdp_mutex);
>>> + } else
>>> + kobject_del(&dev->kobj);
>>> put_device(parent);
>>> }
>>> EXPORT_SYMBOL_GPL(device_del);
>>>
>>> --------------------------->8-----------------------------------
>>
>>
>> OK, one simpler way is to move cleanup_device_parent(dev)
>> after kobject_del(&dev->kobj), which looks more clean too.
>>
> No, We can't move that, bcz kobject_del(&dev->kobj) will clear the parent.
Yeah, but I think it is better to do that and just call
cleanup_glue_dir() directly
because cleanup_device_parent() should have released the glue_dir.
BTW, failure path of device_add() has been broken already.
>
>
>>>
>>>
>>>>>
>>>>>>
>>>>>> [21147.455038] ------------[ cut here ]------------
>>>>>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
>>>>>> kobject_get+0x50/0x68()
>>>>>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>>> qcrypto_module(O)
>>>>>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
>>>>>> [21147.481296] Call trace:
>>>>>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
>>>>>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
>>>>>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
>>>>>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
>>>>>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
>>>>>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
>>>>>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
>>>>>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
>>>>>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>>> [21147.481490] [<ffffffc00061c65c>]
>>>>>> __async_dev_cache_fw_image+0x14/0x54
>>>>>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>>>>>>
>>>>>> [21147.486436] Unable to handle kernel paging request at virtual
>>>>>> address
>>>>>> 0x6b6b6b6b6b6b6bcb
>>>>>> [21147.493816] pgd = ffffffc0a982d000
>>>>>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
>>>>>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>>>>>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>>> qcrypto_module(O)
>>>>>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
>>>>>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
>>>>>> ffffffc007880000
>>>>>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
>>>>>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
>>>>>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>]
>>>>>> pstate:
>>>>>> 80000145
>>>>>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
>>>>>> 0xffffffc007880058)
>>>>>> [21148.003673] Call trace:
>>>>>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
>>>>>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
>>>>>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
>>>>>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
>>>>>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>>> [21148.044822] [<ffffffc00061c65c>]
>>>>>> __async_dev_cache_fw_image+0x14/0x54
>>>>>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
>>>>>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>>>>>>
>>>>>> Below is the callstack where the parent is freed from the slub_debug
>>>>>> info.
>>>>>> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
>>>>>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
>>>>>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
>>>>>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
>>>>>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
>>>>>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
>>>>>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
>>>>>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
>>>>>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
>>>>>> 0xFFFFFFC00061C524
>>>>>> \\vmlinux\firmware_class\_request_firmware\out+0x71C
>>>>>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
>>>>>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
>>>>>> 0xFFFFFFC00061C65C
>>>>>> \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
>>>>>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
>>>>>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
>>>>>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
>>>>>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>>>>>>
>>>>>> For similar type of issue, I see there is an existing fix: "sysfs:
>>>>>> driver
>>>>>> core: Fix glue dir race condition by gdp_mutex".
>>>>>>
>>>>>>
>>>>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>>>>>>
>>>>>> Still I am able to reproduce the issue. I have verified this race on
>>>>>> kernels: 3.10, 3.18 and 4.4.
>>>>>>
>>>>>> I followed below procedure to reproduce the issue:
>>>>>> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
>>>>>> 2. Use test_firmware, modified the test for async calls
>>>>>> 3. Replace WARN_ON with BUG_ON in kref_get().
>>>>>> I ran below script from shell:
>>>>>> count=0
>>>>>> while [ 1 ]
>>>>>> do
>>>>>> echo 3 >
>>>>>> /sys/devices/virtual/misc/test_firmware/trigger_ufw
>>>>>> if [ $? -ne 0 ]; then
>>>>>> print "Exiting.. "
>>>>>> exit 1
>>>>>> fi
>>>>>> count=$(($count +1))
>>>>>> echo "count $count"
>>>>>> done
>>>>>>
>>>>>> With below patch, I could reproduce the issue in the 2nd iteration.
>>>>>
>>>>>
>>>>>
>>>>> I will run your test script to see if there is new findings.
>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> -------------------------8<----------------------------------------------
>>>>>>
>>>>>> To reproduce the race condition, use firmware test and
>>>>>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
>>>>>> releases. So that we can catch the bug easily.
>>>>>>
>>>>>> Enabled below flags in kernel config file:
>>>>>>
>>>>>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
>>>>>> +CONFIG_TEST_FIRMWARE=y
>>>>>
>>>>>
>>>>>
>>>>> Looks I can't reproduce the issue with your approach.
>>>>>
>>>>>>
>>>>>>
>>>>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
>>>>>> index 484604d..727fb24 100644
>>>>>> --- a/include/linux/kref.h
>>>>>> +++ b/include/linux/kref.h
>>>>>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
>>>>>> * condition when this kref is freeing by some other thread
>>>>>> right
>>>>>> now.
>>>>>> * In this case one should use kref_get_unless_zero()
>>>>>> */
>>>>>> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
>>>>>> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
>>>>>> }
>>>>>>
>>>>>> /**
>>>>>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>>>>>> old mode 100644
>>>>>> new mode 100755
>>>>>> index 86374c1..14c9598
>>>>>> --- a/lib/test_firmware.c
>>>>>> +++ b/lib/test_firmware.c
>>>>>> @@ -18,6 +18,7 @@
>>>>>> #include <linux/miscdevice.h>
>>>>>> #include <linux/slab.h>
>>>>>> #include <linux/uaccess.h>
>>>>>> +#include <linux/async.h>
>>>>>>
>>>>>> +
>>>>>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
>>>>>> +
>>>>>> +static void __async_ufw_work(void *name,
>>>>>> + async_cookie_t cookie)
>>>>>> +{
>>>>>> + const struct firmware *fw;
>>>>>> + const char *fw_name = name;
>>>>>> + int ret;
>>>>>> +
>>>>>> + pr_err("requesting %s\n", fw_name);
>>>>>> +
>>>>>> + ret = request_firmware(&fw, fw_name, NULL);
>>>>>> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
>>>>>> + if (!ret)
>>>>>> + kfree(fw);
>>>>>> +
>>>>>> +}
>>>>>> +
>>>>>> +static char *name[] = { "fw1.bin", "fw2.bin"};
>>>>>> +
>>>>>> +static ssize_t trigger_ufw_store(struct device *dev,
>>>>>> + struct device_attribute *attr,
>>>>>> + const char *buf, size_t count)
>>>>>> +{
>>>>>> + int rc, i, c=0;
>>>>>> + u32 start;
>>>>>> + char *fw_name;
>>>>>> +
>>>>>> + rc = kstrtou32(buf, 0, &start);
>>>>>> + if (rc){
>>>>>> + pr_err("Invalid option\n");
>>>>>> + return rc;
>>>>>> + }
>>>>>> + pr_err(" no of iterations %d\n", start);
>>>>>> +
>>>>>> + for (i=0; i< start; i++)
>>>>>> + {
>>>>>> + if (c >= 2)
>>>>>> + c = 0;
>>>>>> + fw_name = name[c++];
>>>>>> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
>>>>>> &ufw_domain);
>>>>>> + }
>>>>>> + async_synchronize_full_domain(&ufw_domain);
>>>>>> + return count;
>>>>>> +}
>>>>>>
>>>>>> static DEVICE_ATTR_WO(trigger_request);
>>>>>> +static DEVICE_ATTR_WO(trigger_ufw);
>>>>>>
>>>>>> static int __init test_firmware_init(void)
>>>>>> {
>>>>>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
>>>>>> goto dereg;
>>>>>> }
>>>>>>
>>>>>> + rc = device_create_file(test_fw_misc_device.this_device,
>>>>>> + &dev_attr_trigger_ufw);
>>>>>> + if (rc) {
>>>>>> + pr_err("could not create sysfs interface: %d\n", rc);
>>>>>> + goto dereg;
>>>>>> + }
>>>>>> pr_warn("interface ready\n");
>>>>>>
>>>>>> return 0;
>>>>>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
>>>>>> {
>>>>>> release_firmware(test_firmware);
>>>>>> device_remove_file(test_fw_misc_device.this_device,
>>>>>> - &dev_attr_trigger_request);
>>>>>> + &dev_attr_trigger_request);
>>>>>> + device_remove_file(test_fw_misc_device.this_device,
>>>>>> + &dev_attr_trigger_ufw);
>>>>>> misc_deregister(&test_fw_misc_device);
>>>>>> pr_warn("removed interface\n");
>>>>>> }
>>>>>>
>>>>>>
>>>>>>
>>>>>> ----------------------------8<--------------------------------------------
>>>>>>
>>>>>> Thanks and regards,
>>>>>> Chandrasekhar L.
>>>>>> --
>>>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>>>> member of
>>>>>> Code Aurora Forum,
>>>>>> a Linux Foundation Collaborative Project.
[toc] | [prev] | [next] | [standalone]
| From | Chandra Sekhar Lingutla <clingutla@codeaurora.org> |
|---|---|
| Date | 2016-03-16 10:10 +0100 |
| Message-ID | <rdfCO-6Vb-11@gated-at.bofh.it> |
| In reply to | #1358754 |
On 03/16/2016 02:28 PM, Ming Lei wrote:
> On Wed, Mar 16, 2016 at 4:48 PM, Chandra Sekhar Lingutla
> <clingutla@codeaurora.org> wrote:
>> On 03/16/2016 02:12 PM, Ming Lei wrote:
>>>
>>> On Wed, Mar 16, 2016 at 3:02 PM, Chandra Sekhar Lingutla
>>> <clingutla@codeaurora.org> wrote:
>>>>
>>>> Hi Ming,
>>>>
>>>>
>>>> On 03/16/2016 07:36 AM, Ming Lei wrote:
>>>>>
>>>>>
>>>>> On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@canonical.com>
>>>>> wrote:
>>>>>>
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
>>>>>>>
>>>>>>>
>>>>>>> Hello,
>>>>>>>
>>>>>>> I see possible race in _request_firmware_load function, on which I
>>>>>>> wanted to
>>>>>>> take your opinion.
>>>>>>>
>>>>>>> When system is going to low power mode, device_cache_fw_images() is
>>>>>>> called
>>>>>>> from pm notifier which schedules asynchronous workers to cache devices
>>>>>>> firmware.
>>>>>>> If more than 2 async requests falls under user helper mode, then there
>>>>>>> is a
>>>>>>> use after free of "firmware" directory kobject.
>>>>>>
>>>>>>
>>>>>>
>>>>>> If two requests are for getting same firmware image, only one can be
>>>>>> sent
>>>>>> out and be completed with user helper, please see
>>>>>> fw_lookup_and_allocate_buf(),
>>>>>> so the race shouldn't have been triggered in this case.
>>>>>>
>>>>>> So I guess your test must be involved with at least two different
>>>>>> requests.
>>>>>>
>>>>>>>
>>>>>>> The race will hit, when one asynchronous worker calls device_del()
>>>>>>> while
>>>>>>> other asynchronous worker calls get_device_parent() in
>>>>>>> _request_firmware_load().
>>>>>>> After loading firmware, first worker calls device_del(), and
>>>>>>> "firmware"
>>>>>>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put()
>>>>>>> with
>>>>>>> gdp_mutex lock held.
>>>>>>> Meanwhile, second async worker calls device_add(), and
>>>>>>> get_device_parent()
>>>>>>> is still able to find the firmware directory kobject in ksets after
>>>>>>> getting
>>>>>>> gdp_mutex.
>>>>>>> This kobject gets added as parent to the second device kobject.
>>>>>>> By the time of accessing the parent kobject, its ref count was 0 and
>>>>>>> prints
>>>>>>> below warning stack followed by crash.
>>>>>>
>>>>>>
>>>>>>
>>>>>> The trick here is just that we don't use 'struct device' in
>>>>>> device_cache_fw_images(),
>>>>>> then the firmware device's parent is null during calling device_add()
>>>>>> from
>>>>>> _request_firmware_load(), but this should be allowed by driver core.
>>>>>>
>>>>>> From firmware class view, both device_add()/device_del() is run with
>>>>>> pair,
>>>>>> and driver core still complains during get_device_parent(), so
>>>>>> something
>>>>>> inside driver core should be be wrong, IMO.
>>>>>
>>>>>
>>>>>
>>>>> Thinking about the issue further, I believe it is a false positive which
>>>>> is
>>>>> caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
>>>>>
>>>>> 1) device_add() path
>>>>>
>>>>> get_device_parent()
>>>>> ......
>>>>> mutex_lock(&gdp_mutex);
>>>>>
>>>>> /* find our class-directory at the parent and
>>>>> reference
>>>>> it */
>>>>> spin_lock(&dev->class->p->glue_dirs.list_lock);
>>>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list,
>>>>> entry)
>>>>> if (k->parent == parent_kobj) {
>>>>> kobj = kobject_get(k);
>>>>> break;
>>>>> }
>>>>> spin_unlock(&dev->class->p->glue_dirs.list_lock);
>>>>> if (kobj) {
>>>>> mutex_unlock(&gdp_mutex);
>>>>> return kobj;
>>>>> }
>>>>> k = class_dir_create_and_add(dev->class, parent_kobj);
>>>>> mutex_unlock(&gdp_mutex);
>>>>> ......
>>>>>
>>>>> 2) device_del() path
>>>>>
>>>>> cleanup_device_parent()
>>>>> ->cleanup_glue_dir()
>>>>> ->mutex_lock(&gdp_mutex);
>>>>> ->kobject_put(glue_dir);
>>>>> ->kobject_cleanup()
>>>>> ->kobject_del()
>>>>> ->kobj_kset_leave()
>>>>> ->mutex_unlock(&gdp_mutex);
>>>>>
>>>>> So gdp_mutex is held wrt. both looking up/adding the parent kobject
>>>>> and removing the parent kobject. Actually with this lock, both glur_dir
>>>>> kobject's referece counting and joining/leaving kset are run atomically.
>>>>>
>>>>> The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
>>>>> which causes kobject_cleanup() to be run in workqueue context and the
>>>>> lock of gdp_mutex can't be hold in that situation anymore. That is the
>>>>> root
>>>>> cause for your race.
>>>>>
>>>>> That also said DEBUG_KOBJECT_RELEASE might cause trouble in
>>>>> some situations.
>>>>>
>>>>> Thanks,
>>>>> Ming
>>>>>
>>>> I agree that, CONFIG_DEBUG_KOBJECT_RELEASE can cause the race, as it
>>>> delays
>>>> call to kobject_cleanup() which deletes kobj entry in glue_dir list.
>>>>
>>>> I see the race even after disabling CONFIG_DEBUG_KOBJECT_RELEASE.
>>>>
>>>> The race is between kobject_put() and kobject_get() for the "firmware"
>>>> directory.
>>>>
>>>> In device_del() path, I see the race after the call of
>>>> cleanup_device_parent().
>>>> cleanup_device_parent() calls kobject_put(glue_dir) with gdp_mutex lock
>>>> holding,
>>>> So ideally, to call kobject_put/kobject_get(glue_dir) we need to acquire
>>>> gdp_mutex.
>>>>
>>>> but kobject_del(kobj) will not hold the gdp_mutex lock while calling
>>>> kobject_put(kobj->parent).
>>>>
>>>> Here is the race:
>>>>
>>>> Consider 2 async works calls request_firmware() for 2 different binaries
>>>> (fw1.bin, fw2.bin)
>>>> Async work1 got scheduled first, and it falls in user helper mode so it
>>>> creates "firmware" dir
>>>> and then creates "fw1.bin" directory to load data from user.
>>>> After load completion or timeout, it starts cleanup dir's, meantime async
>>>> work2 got scheduled and
>>>> it also falls in user helper mode, and story starts here:
>>>>
>>>> PATH1 req fw for "fw1.bin"
>>>> PATH2
>>>> req fw for "fw2.bin"
>>>> _request_firmware_load()
>>>> device_del(dev1)
>>>>
>>>> ->cleanup_device_parent()
>>>>
>>>> mutex_lock(&gdp_mutex);
>>>>
>>>> _request_firmware_load("fw2.bin")
>>>> kobject_put(kobj->parent); --> firmware ref ->1
>>>> ->device_add(dev2)
>>>> mutex_unlock(&gdp_mutex);
>>>> ->get_device_parent()
>>>> ->kobject_del()
>>>> mutex_lock(&gdp_mutex)
>>>> kobj_kset_leave(kobj); -->del "fw1.bin" kobj in kset
>>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
>>>> kobject_put(kobj->parent); /* No lock :)*/
>>>> if (k->parent == parent_kobj) {
>>>>
>>>> ->kref_put() --> firmware ref ->0
>>>> kobj = kobject_get(k); -> k is "firmware"
>>>> dir
>>>> ->kboject_release()
>>>> break;
>>>>
>>>> ->kobject_del()
>>>> }
>>>>
>>>> /*here deletes firmware entry in kset*/
>>>> mutex_unlock(&gdp_mutex)
>>>>
>>>> ->dev2->kobj.parent = kobj -> kobj is released already
>>>>
>>>>
>>>>
>>>> PATH 1 is started removing the kobject of "fw1.bin" and its parent
>>>> "firmware"
>>>> .
>>>> cleanup_device_parent(dev1) makes firmware ref count to 1, by calling
>>>> kobject_put(firmware) with gdp_mutex held.
>>>>
>>>> and kobject_del(dev1->kobj) will again calls kobject_put(kobj->parent)
>>>> without holding gdp_mutex.
>>>>
>>>> In PATH2, glue_dir is able to find "firmware" kobj, as firmware dir kobj
>>>> is
>>>> deleted from the glue_dir list at kboject_release().
>>>> and it calls kobject_get(firmware), by the time PATH1 calls
>>>> kobject_release(firmware).
>>>>
>>>> So PATH2 got reference of freed firmware kobj and added as parent to
>>>> "fw2.bin" kobj.
>>>>
>>>> I think, here is possible fix for this race:
>>>>
>>>> ------------------------8<-------------------------------------
>>>> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
>>>>
>>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>>>> index 5d8b713..47bc082 100644
>>>> --- a/drivers/base/core.c
>>>> +++ b/drivers/base/core.c
>>>> @@ -1224,7 +1224,13 @@ void device_del(struct device *dev)
>>>> BUS_NOTIFY_REMOVED_DEVICE,
>>>> dev);
>>>> kobject_uevent(&dev->kobj, KOBJ_REMOVE);
>>>> cleanup_device_parent(dev);
>>>> - kobject_del(&dev->kobj);
>>>> +
>>>> + if (dev->kobj.parent->kset == &dev->class->p->glue_dirs) {
>>>> + mutex_lock(&gdp_mutex);
>>>> + kobject_del(&dev->kobj);
>>>> + mutex_unlock(&gdp_mutex);
>>>> + } else
>>>> + kobject_del(&dev->kobj);
>>>> put_device(parent);
>>>> }
>>>> EXPORT_SYMBOL_GPL(device_del);
>>>>
>>>> --------------------------->8-----------------------------------
>>>
>>>
>>> OK, one simpler way is to move cleanup_device_parent(dev)
>>> after kobject_del(&dev->kobj), which looks more clean too.
>>>
>> No, We can't move that, bcz kobject_del(&dev->kobj) will clear the parent.
>
> Yeah, but I think it is better to do that and just call
> cleanup_glue_dir() directly
> because cleanup_device_parent() should have released the glue_dir.
>
> BTW, failure path of device_add() has been broken already.
>
Yah, forgot to mention that. we need to reorder like above fix, can we?.
>>
>>
>>>>
>>>>
>>>>>>
>>>>>>>
>>>>>>> [21147.455038] ------------[ cut here ]------------
>>>>>>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
>>>>>>> kobject_get+0x50/0x68()
>>>>>>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>>>> qcrypto_module(O)
>>>>>>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>>>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
>>>>>>> [21147.481296] Call trace:
>>>>>>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
>>>>>>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
>>>>>>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
>>>>>>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
>>>>>>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
>>>>>>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
>>>>>>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
>>>>>>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
>>>>>>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>>>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>>>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>>>> [21147.481490] [<ffffffc00061c65c>]
>>>>>>> __async_dev_cache_fw_image+0x14/0x54
>>>>>>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>>>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>>>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>>>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>>>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>>>>>>>
>>>>>>> [21147.486436] Unable to handle kernel paging request at virtual
>>>>>>> address
>>>>>>> 0x6b6b6b6b6b6b6bcb
>>>>>>> [21147.493816] pgd = ffffffc0a982d000
>>>>>>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
>>>>>>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>>>>>>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>>>> qcrypto_module(O)
>>>>>>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>>>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
>>>>>>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
>>>>>>> ffffffc007880000
>>>>>>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
>>>>>>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
>>>>>>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>]
>>>>>>> pstate:
>>>>>>> 80000145
>>>>>>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
>>>>>>> 0xffffffc007880058)
>>>>>>> [21148.003673] Call trace:
>>>>>>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
>>>>>>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
>>>>>>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
>>>>>>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
>>>>>>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>>>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>>>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>>>> [21148.044822] [<ffffffc00061c65c>]
>>>>>>> __async_dev_cache_fw_image+0x14/0x54
>>>>>>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>>>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>>>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>>>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>>>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
>>>>>>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>>>>>>>
>>>>>>> Below is the callstack where the parent is freed from the slub_debug
>>>>>>> info.
>>>>>>> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
>>>>>>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
>>>>>>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
>>>>>>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
>>>>>>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
>>>>>>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
>>>>>>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
>>>>>>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
>>>>>>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
>>>>>>> 0xFFFFFFC00061C524
>>>>>>> \\vmlinux\firmware_class\_request_firmware\out+0x71C
>>>>>>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
>>>>>>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
>>>>>>> 0xFFFFFFC00061C65C
>>>>>>> \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
>>>>>>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
>>>>>>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
>>>>>>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
>>>>>>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>>>>>>>
>>>>>>> For similar type of issue, I see there is an existing fix: "sysfs:
>>>>>>> driver
>>>>>>> core: Fix glue dir race condition by gdp_mutex".
>>>>>>>
>>>>>>>
>>>>>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>>>>>>>
>>>>>>> Still I am able to reproduce the issue. I have verified this race on
>>>>>>> kernels: 3.10, 3.18 and 4.4.
>>>>>>>
>>>>>>> I followed below procedure to reproduce the issue:
>>>>>>> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
>>>>>>> 2. Use test_firmware, modified the test for async calls
>>>>>>> 3. Replace WARN_ON with BUG_ON in kref_get().
>>>>>>> I ran below script from shell:
>>>>>>> count=0
>>>>>>> while [ 1 ]
>>>>>>> do
>>>>>>> echo 3 >
>>>>>>> /sys/devices/virtual/misc/test_firmware/trigger_ufw
>>>>>>> if [ $? -ne 0 ]; then
>>>>>>> print "Exiting.. "
>>>>>>> exit 1
>>>>>>> fi
>>>>>>> count=$(($count +1))
>>>>>>> echo "count $count"
>>>>>>> done
>>>>>>>
>>>>>>> With below patch, I could reproduce the issue in the 2nd iteration.
>>>>>>
>>>>>>
>>>>>>
>>>>>> I will run your test script to see if there is new findings.
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> -------------------------8<----------------------------------------------
>>>>>>>
>>>>>>> To reproduce the race condition, use firmware test and
>>>>>>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
>>>>>>> releases. So that we can catch the bug easily.
>>>>>>>
>>>>>>> Enabled below flags in kernel config file:
>>>>>>>
>>>>>>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
>>>>>>> +CONFIG_TEST_FIRMWARE=y
>>>>>>
>>>>>>
>>>>>>
>>>>>> Looks I can't reproduce the issue with your approach.
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
>>>>>>> index 484604d..727fb24 100644
>>>>>>> --- a/include/linux/kref.h
>>>>>>> +++ b/include/linux/kref.h
>>>>>>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
>>>>>>> * condition when this kref is freeing by some other thread
>>>>>>> right
>>>>>>> now.
>>>>>>> * In this case one should use kref_get_unless_zero()
>>>>>>> */
>>>>>>> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
>>>>>>> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
>>>>>>> }
>>>>>>>
>>>>>>> /**
>>>>>>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>>>>>>> old mode 100644
>>>>>>> new mode 100755
>>>>>>> index 86374c1..14c9598
>>>>>>> --- a/lib/test_firmware.c
>>>>>>> +++ b/lib/test_firmware.c
>>>>>>> @@ -18,6 +18,7 @@
>>>>>>> #include <linux/miscdevice.h>
>>>>>>> #include <linux/slab.h>
>>>>>>> #include <linux/uaccess.h>
>>>>>>> +#include <linux/async.h>
>>>>>>>
>>>>>>> +
>>>>>>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
>>>>>>> +
>>>>>>> +static void __async_ufw_work(void *name,
>>>>>>> + async_cookie_t cookie)
>>>>>>> +{
>>>>>>> + const struct firmware *fw;
>>>>>>> + const char *fw_name = name;
>>>>>>> + int ret;
>>>>>>> +
>>>>>>> + pr_err("requesting %s\n", fw_name);
>>>>>>> +
>>>>>>> + ret = request_firmware(&fw, fw_name, NULL);
>>>>>>> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
>>>>>>> + if (!ret)
>>>>>>> + kfree(fw);
>>>>>>> +
>>>>>>> +}
>>>>>>> +
>>>>>>> +static char *name[] = { "fw1.bin", "fw2.bin"};
>>>>>>> +
>>>>>>> +static ssize_t trigger_ufw_store(struct device *dev,
>>>>>>> + struct device_attribute *attr,
>>>>>>> + const char *buf, size_t count)
>>>>>>> +{
>>>>>>> + int rc, i, c=0;
>>>>>>> + u32 start;
>>>>>>> + char *fw_name;
>>>>>>> +
>>>>>>> + rc = kstrtou32(buf, 0, &start);
>>>>>>> + if (rc){
>>>>>>> + pr_err("Invalid option\n");
>>>>>>> + return rc;
>>>>>>> + }
>>>>>>> + pr_err(" no of iterations %d\n", start);
>>>>>>> +
>>>>>>> + for (i=0; i< start; i++)
>>>>>>> + {
>>>>>>> + if (c >= 2)
>>>>>>> + c = 0;
>>>>>>> + fw_name = name[c++];
>>>>>>> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
>>>>>>> &ufw_domain);
>>>>>>> + }
>>>>>>> + async_synchronize_full_domain(&ufw_domain);
>>>>>>> + return count;
>>>>>>> +}
>>>>>>>
>>>>>>> static DEVICE_ATTR_WO(trigger_request);
>>>>>>> +static DEVICE_ATTR_WO(trigger_ufw);
>>>>>>>
>>>>>>> static int __init test_firmware_init(void)
>>>>>>> {
>>>>>>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
>>>>>>> goto dereg;
>>>>>>> }
>>>>>>>
>>>>>>> + rc = device_create_file(test_fw_misc_device.this_device,
>>>>>>> + &dev_attr_trigger_ufw);
>>>>>>> + if (rc) {
>>>>>>> + pr_err("could not create sysfs interface: %d\n", rc);
>>>>>>> + goto dereg;
>>>>>>> + }
>>>>>>> pr_warn("interface ready\n");
>>>>>>>
>>>>>>> return 0;
>>>>>>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
>>>>>>> {
>>>>>>> release_firmware(test_firmware);
>>>>>>> device_remove_file(test_fw_misc_device.this_device,
>>>>>>> - &dev_attr_trigger_request);
>>>>>>> + &dev_attr_trigger_request);
>>>>>>> + device_remove_file(test_fw_misc_device.this_device,
>>>>>>> + &dev_attr_trigger_ufw);
>>>>>>> misc_deregister(&test_fw_misc_device);
>>>>>>> pr_warn("removed interface\n");
>>>>>>> }
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> ----------------------------8<--------------------------------------------
>>>>>>>
>>>>>>> Thanks and regards,
>>>>>>> Chandrasekhar L.
>>>>>>> --
>>>>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>>>>> member of
>>>>>>> Code Aurora Forum,
>>>>>>> a Linux Foundation Collaborative Project.
[toc] | [prev] | [next] | [standalone]
| From | Chandra Sekhar Lingutla <clingutla@codeaurora.org> |
|---|---|
| Date | 2016-03-16 11:00 +0100 |
| Message-ID | <rdgpc-7eq-5@gated-at.bofh.it> |
| In reply to | #1358758 |
Hi Ming,
On 03/16/2016 02:34 PM, Chandra Sekhar Lingutla wrote:
> On 03/16/2016 02:28 PM, Ming Lei wrote:
>> On Wed, Mar 16, 2016 at 4:48 PM, Chandra Sekhar Lingutla
>> <clingutla@codeaurora.org> wrote:
>>> On 03/16/2016 02:12 PM, Ming Lei wrote:
>>>>
>>>> On Wed, Mar 16, 2016 at 3:02 PM, Chandra Sekhar Lingutla
>>>> <clingutla@codeaurora.org> wrote:
>>>>>
>>>>> Hi Ming,
>>>>>
>>>>>
>>>>> On 03/16/2016 07:36 AM, Ming Lei wrote:
>>>>>>
>>>>>>
>>>>>> On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@canonical.com>
>>>>>> wrote:
>>>>>>>
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> Hello,
>>>>>>>>
>>>>>>>> I see possible race in _request_firmware_load function, on which I
>>>>>>>> wanted to
>>>>>>>> take your opinion.
>>>>>>>>
>>>>>>>> When system is going to low power mode, device_cache_fw_images() is
>>>>>>>> called
>>>>>>>> from pm notifier which schedules asynchronous workers to cache devices
>>>>>>>> firmware.
>>>>>>>> If more than 2 async requests falls under user helper mode, then there
>>>>>>>> is a
>>>>>>>> use after free of "firmware" directory kobject.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> If two requests are for getting same firmware image, only one can be
>>>>>>> sent
>>>>>>> out and be completed with user helper, please see
>>>>>>> fw_lookup_and_allocate_buf(),
>>>>>>> so the race shouldn't have been triggered in this case.
>>>>>>>
>>>>>>> So I guess your test must be involved with at least two different
>>>>>>> requests.
>>>>>>>
>>>>>>>>
>>>>>>>> The race will hit, when one asynchronous worker calls device_del()
>>>>>>>> while
>>>>>>>> other asynchronous worker calls get_device_parent() in
>>>>>>>> _request_firmware_load().
>>>>>>>> After loading firmware, first worker calls device_del(), and
>>>>>>>> "firmware"
>>>>>>>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put()
>>>>>>>> with
>>>>>>>> gdp_mutex lock held.
>>>>>>>> Meanwhile, second async worker calls device_add(), and
>>>>>>>> get_device_parent()
>>>>>>>> is still able to find the firmware directory kobject in ksets after
>>>>>>>> getting
>>>>>>>> gdp_mutex.
>>>>>>>> This kobject gets added as parent to the second device kobject.
>>>>>>>> By the time of accessing the parent kobject, its ref count was 0 and
>>>>>>>> prints
>>>>>>>> below warning stack followed by crash.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> The trick here is just that we don't use 'struct device' in
>>>>>>> device_cache_fw_images(),
>>>>>>> then the firmware device's parent is null during calling device_add()
>>>>>>> from
>>>>>>> _request_firmware_load(), but this should be allowed by driver core.
>>>>>>>
>>>>>>> From firmware class view, both device_add()/device_del() is run with
>>>>>>> pair,
>>>>>>> and driver core still complains during get_device_parent(), so
>>>>>>> something
>>>>>>> inside driver core should be be wrong, IMO.
>>>>>>
>>>>>>
>>>>>>
>>>>>> Thinking about the issue further, I believe it is a false positive which
>>>>>> is
>>>>>> caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
>>>>>>
>>>>>> 1) device_add() path
>>>>>>
>>>>>> get_device_parent()
>>>>>> ......
>>>>>> mutex_lock(&gdp_mutex);
>>>>>>
>>>>>> /* find our class-directory at the parent and
>>>>>> reference
>>>>>> it */
>>>>>> spin_lock(&dev->class->p->glue_dirs.list_lock);
>>>>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list,
>>>>>> entry)
>>>>>> if (k->parent == parent_kobj) {
>>>>>> kobj = kobject_get(k);
>>>>>> break;
>>>>>> }
>>>>>> spin_unlock(&dev->class->p->glue_dirs.list_lock);
>>>>>> if (kobj) {
>>>>>> mutex_unlock(&gdp_mutex);
>>>>>> return kobj;
>>>>>> }
>>>>>> k = class_dir_create_and_add(dev->class, parent_kobj);
>>>>>> mutex_unlock(&gdp_mutex);
>>>>>> ......
>>>>>>
>>>>>> 2) device_del() path
>>>>>>
>>>>>> cleanup_device_parent()
>>>>>> ->cleanup_glue_dir()
>>>>>> ->mutex_lock(&gdp_mutex);
>>>>>> ->kobject_put(glue_dir);
>>>>>> ->kobject_cleanup()
>>>>>> ->kobject_del()
>>>>>> ->kobj_kset_leave()
>>>>>> ->mutex_unlock(&gdp_mutex);
>>>>>>
>>>>>> So gdp_mutex is held wrt. both looking up/adding the parent kobject
>>>>>> and removing the parent kobject. Actually with this lock, both glur_dir
>>>>>> kobject's referece counting and joining/leaving kset are run atomically.
>>>>>>
>>>>>> The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
>>>>>> which causes kobject_cleanup() to be run in workqueue context and the
>>>>>> lock of gdp_mutex can't be hold in that situation anymore. That is the
>>>>>> root
>>>>>> cause for your race.
>>>>>>
>>>>>> That also said DEBUG_KOBJECT_RELEASE might cause trouble in
>>>>>> some situations.
>>>>>>
>>>>>> Thanks,
>>>>>> Ming
>>>>>>
>>>>> I agree that, CONFIG_DEBUG_KOBJECT_RELEASE can cause the race, as it
>>>>> delays
>>>>> call to kobject_cleanup() which deletes kobj entry in glue_dir list.
>>>>>
>>>>> I see the race even after disabling CONFIG_DEBUG_KOBJECT_RELEASE.
>>>>>
>>>>> The race is between kobject_put() and kobject_get() for the "firmware"
>>>>> directory.
>>>>>
>>>>> In device_del() path, I see the race after the call of
>>>>> cleanup_device_parent().
>>>>> cleanup_device_parent() calls kobject_put(glue_dir) with gdp_mutex lock
>>>>> holding,
>>>>> So ideally, to call kobject_put/kobject_get(glue_dir) we need to acquire
>>>>> gdp_mutex.
>>>>>
>>>>> but kobject_del(kobj) will not hold the gdp_mutex lock while calling
>>>>> kobject_put(kobj->parent).
>>>>>
>>>>> Here is the race:
>>>>>
>>>>> Consider 2 async works calls request_firmware() for 2 different binaries
>>>>> (fw1.bin, fw2.bin)
>>>>> Async work1 got scheduled first, and it falls in user helper mode so it
>>>>> creates "firmware" dir
>>>>> and then creates "fw1.bin" directory to load data from user.
>>>>> After load completion or timeout, it starts cleanup dir's, meantime async
>>>>> work2 got scheduled and
>>>>> it also falls in user helper mode, and story starts here:
>>>>>
>>>>> PATH1 req fw for "fw1.bin"
>>>>> PATH2
>>>>> req fw for "fw2.bin"
>>>>> _request_firmware_load()
>>>>> device_del(dev1)
>>>>>
>>>>> ->cleanup_device_parent()
>>>>>
>>>>> mutex_lock(&gdp_mutex);
>>>>>
>>>>> _request_firmware_load("fw2.bin")
>>>>> kobject_put(kobj->parent); --> firmware ref ->1
>>>>> ->device_add(dev2)
>>>>> mutex_unlock(&gdp_mutex);
>>>>> ->get_device_parent()
>>>>> ->kobject_del()
>>>>> mutex_lock(&gdp_mutex)
>>>>> kobj_kset_leave(kobj); -->del "fw1.bin" kobj in kset
>>>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
>>>>> kobject_put(kobj->parent); /* No lock :)*/
>>>>> if (k->parent == parent_kobj) {
>>>>>
>>>>> ->kref_put() --> firmware ref ->0
>>>>> kobj = kobject_get(k); -> k is "firmware"
>>>>> dir
>>>>> ->kboject_release()
>>>>> break;
>>>>>
>>>>> ->kobject_del()
>>>>> }
>>>>>
>>>>> /*here deletes firmware entry in kset*/
>>>>> mutex_unlock(&gdp_mutex)
>>>>>
>>>>> ->dev2->kobj.parent = kobj -> kobj is released already
>>>>>
>>>>>
>>>>>
>>>>> PATH 1 is started removing the kobject of "fw1.bin" and its parent
>>>>> "firmware"
>>>>> .
>>>>> cleanup_device_parent(dev1) makes firmware ref count to 1, by calling
>>>>> kobject_put(firmware) with gdp_mutex held.
>>>>>
>>>>> and kobject_del(dev1->kobj) will again calls kobject_put(kobj->parent)
>>>>> without holding gdp_mutex.
>>>>>
>>>>> In PATH2, glue_dir is able to find "firmware" kobj, as firmware dir kobj
>>>>> is
>>>>> deleted from the glue_dir list at kboject_release().
>>>>> and it calls kobject_get(firmware), by the time PATH1 calls
>>>>> kobject_release(firmware).
>>>>>
>>>>> So PATH2 got reference of freed firmware kobj and added as parent to
>>>>> "fw2.bin" kobj.
>>>>>
>>>>> I think, here is possible fix for this race:
>>>>>
>>>>> ------------------------8<-------------------------------------
>>>>> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
>>>>>
>>>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>>>>> index 5d8b713..47bc082 100644
>>>>> --- a/drivers/base/core.c
>>>>> +++ b/drivers/base/core.c
>>>>> @@ -1224,7 +1224,13 @@ void device_del(struct device *dev)
>>>>> BUS_NOTIFY_REMOVED_DEVICE,
>>>>> dev);
>>>>> kobject_uevent(&dev->kobj, KOBJ_REMOVE);
>>>>> cleanup_device_parent(dev);
>>>>> - kobject_del(&dev->kobj);
>>>>> +
>>>>> + if (dev->kobj.parent->kset == &dev->class->p->glue_dirs) {
>>>>> + mutex_lock(&gdp_mutex);
>>>>> + kobject_del(&dev->kobj);
>>>>> + mutex_unlock(&gdp_mutex);
>>>>> + } else
>>>>> + kobject_del(&dev->kobj);
>>>>> put_device(parent);
>>>>> }
>>>>> EXPORT_SYMBOL_GPL(device_del);
>>>>>
>>>>> --------------------------->8-----------------------------------
>>>>
>>>>
>>>> OK, one simpler way is to move cleanup_device_parent(dev)
>>>> after kobject_del(&dev->kobj), which looks more clean too.
>>>>
>>> No, We can't move that, bcz kobject_del(&dev->kobj) will clear the parent.
>>
>> Yeah, but I think it is better to do that and just call
>> cleanup_glue_dir() directly
>> because cleanup_device_parent() should have released the glue_dir.
>>
Sorry, i am not able understand correctly, If we reorder kobje_del and cleanup_device_parent(),
kobject_del() clears kobj->parent, and cleanup_device_parent() gets glue_dir with dev->kobj->parent(),
cleanup_glue_dir() returns without calling kobject_put() as glue_dir is NULL, so firmware dir becomes dangling kobj.
Am I missing something here?
>> BTW, failure path of device_add() has been broken already.
>>
> Yah, forgot to mention that. we need to reorder like above fix, can we?.
>
>>>
>>>
>>>>>
>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> [21147.455038] ------------[ cut here ]------------
>>>>>>>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
>>>>>>>> kobject_get+0x50/0x68()
>>>>>>>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>>>>> qcrypto_module(O)
>>>>>>>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>>>>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
>>>>>>>> [21147.481296] Call trace:
>>>>>>>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
>>>>>>>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
>>>>>>>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
>>>>>>>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
>>>>>>>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
>>>>>>>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
>>>>>>>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
>>>>>>>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
>>>>>>>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>>>>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>>>>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>>>>> [21147.481490] [<ffffffc00061c65c>]
>>>>>>>> __async_dev_cache_fw_image+0x14/0x54
>>>>>>>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>>>>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>>>>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>>>>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>>>>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>>>>>>>>
>>>>>>>> [21147.486436] Unable to handle kernel paging request at virtual
>>>>>>>> address
>>>>>>>> 0x6b6b6b6b6b6b6bcb
>>>>>>>> [21147.493816] pgd = ffffffc0a982d000
>>>>>>>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
>>>>>>>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>>>>>>>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>>>>> qcrypto_module(O)
>>>>>>>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>>>>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
>>>>>>>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
>>>>>>>> ffffffc007880000
>>>>>>>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
>>>>>>>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
>>>>>>>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>]
>>>>>>>> pstate:
>>>>>>>> 80000145
>>>>>>>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
>>>>>>>> 0xffffffc007880058)
>>>>>>>> [21148.003673] Call trace:
>>>>>>>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
>>>>>>>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
>>>>>>>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
>>>>>>>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
>>>>>>>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>>>>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>>>>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>>>>> [21148.044822] [<ffffffc00061c65c>]
>>>>>>>> __async_dev_cache_fw_image+0x14/0x54
>>>>>>>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>>>>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>>>>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>>>>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>>>>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
>>>>>>>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>>>>>>>>
>>>>>>>> Below is the callstack where the parent is freed from the slub_debug
>>>>>>>> info.
>>>>>>>> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
>>>>>>>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
>>>>>>>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
>>>>>>>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
>>>>>>>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
>>>>>>>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
>>>>>>>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
>>>>>>>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
>>>>>>>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
>>>>>>>> 0xFFFFFFC00061C524
>>>>>>>> \\vmlinux\firmware_class\_request_firmware\out+0x71C
>>>>>>>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
>>>>>>>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
>>>>>>>> 0xFFFFFFC00061C65C
>>>>>>>> \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
>>>>>>>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
>>>>>>>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
>>>>>>>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
>>>>>>>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>>>>>>>>
>>>>>>>> For similar type of issue, I see there is an existing fix: "sysfs:
>>>>>>>> driver
>>>>>>>> core: Fix glue dir race condition by gdp_mutex".
>>>>>>>>
>>>>>>>>
>>>>>>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>>>>>>>>
>>>>>>>> Still I am able to reproduce the issue. I have verified this race on
>>>>>>>> kernels: 3.10, 3.18 and 4.4.
>>>>>>>>
>>>>>>>> I followed below procedure to reproduce the issue:
>>>>>>>> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
>>>>>>>> 2. Use test_firmware, modified the test for async calls
>>>>>>>> 3. Replace WARN_ON with BUG_ON in kref_get().
>>>>>>>> I ran below script from shell:
>>>>>>>> count=0
>>>>>>>> while [ 1 ]
>>>>>>>> do
>>>>>>>> echo 3 >
>>>>>>>> /sys/devices/virtual/misc/test_firmware/trigger_ufw
>>>>>>>> if [ $? -ne 0 ]; then
>>>>>>>> print "Exiting.. "
>>>>>>>> exit 1
>>>>>>>> fi
>>>>>>>> count=$(($count +1))
>>>>>>>> echo "count $count"
>>>>>>>> done
>>>>>>>>
>>>>>>>> With below patch, I could reproduce the issue in the 2nd iteration.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> I will run your test script to see if there is new findings.
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> -------------------------8<----------------------------------------------
>>>>>>>>
>>>>>>>> To reproduce the race condition, use firmware test and
>>>>>>>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
>>>>>>>> releases. So that we can catch the bug easily.
>>>>>>>>
>>>>>>>> Enabled below flags in kernel config file:
>>>>>>>>
>>>>>>>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
>>>>>>>> +CONFIG_TEST_FIRMWARE=y
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Looks I can't reproduce the issue with your approach.
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
>>>>>>>> index 484604d..727fb24 100644
>>>>>>>> --- a/include/linux/kref.h
>>>>>>>> +++ b/include/linux/kref.h
>>>>>>>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
>>>>>>>> * condition when this kref is freeing by some other thread
>>>>>>>> right
>>>>>>>> now.
>>>>>>>> * In this case one should use kref_get_unless_zero()
>>>>>>>> */
>>>>>>>> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
>>>>>>>> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
>>>>>>>> }
>>>>>>>>
>>>>>>>> /**
>>>>>>>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>>>>>>>> old mode 100644
>>>>>>>> new mode 100755
>>>>>>>> index 86374c1..14c9598
>>>>>>>> --- a/lib/test_firmware.c
>>>>>>>> +++ b/lib/test_firmware.c
>>>>>>>> @@ -18,6 +18,7 @@
>>>>>>>> #include <linux/miscdevice.h>
>>>>>>>> #include <linux/slab.h>
>>>>>>>> #include <linux/uaccess.h>
>>>>>>>> +#include <linux/async.h>
>>>>>>>>
>>>>>>>> +
>>>>>>>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
>>>>>>>> +
>>>>>>>> +static void __async_ufw_work(void *name,
>>>>>>>> + async_cookie_t cookie)
>>>>>>>> +{
>>>>>>>> + const struct firmware *fw;
>>>>>>>> + const char *fw_name = name;
>>>>>>>> + int ret;
>>>>>>>> +
>>>>>>>> + pr_err("requesting %s\n", fw_name);
>>>>>>>> +
>>>>>>>> + ret = request_firmware(&fw, fw_name, NULL);
>>>>>>>> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
>>>>>>>> + if (!ret)
>>>>>>>> + kfree(fw);
>>>>>>>> +
>>>>>>>> +}
>>>>>>>> +
>>>>>>>> +static char *name[] = { "fw1.bin", "fw2.bin"};
>>>>>>>> +
>>>>>>>> +static ssize_t trigger_ufw_store(struct device *dev,
>>>>>>>> + struct device_attribute *attr,
>>>>>>>> + const char *buf, size_t count)
>>>>>>>> +{
>>>>>>>> + int rc, i, c=0;
>>>>>>>> + u32 start;
>>>>>>>> + char *fw_name;
>>>>>>>> +
>>>>>>>> + rc = kstrtou32(buf, 0, &start);
>>>>>>>> + if (rc){
>>>>>>>> + pr_err("Invalid option\n");
>>>>>>>> + return rc;
>>>>>>>> + }
>>>>>>>> + pr_err(" no of iterations %d\n", start);
>>>>>>>> +
>>>>>>>> + for (i=0; i< start; i++)
>>>>>>>> + {
>>>>>>>> + if (c >= 2)
>>>>>>>> + c = 0;
>>>>>>>> + fw_name = name[c++];
>>>>>>>> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
>>>>>>>> &ufw_domain);
>>>>>>>> + }
>>>>>>>> + async_synchronize_full_domain(&ufw_domain);
>>>>>>>> + return count;
>>>>>>>> +}
>>>>>>>>
>>>>>>>> static DEVICE_ATTR_WO(trigger_request);
>>>>>>>> +static DEVICE_ATTR_WO(trigger_ufw);
>>>>>>>>
>>>>>>>> static int __init test_firmware_init(void)
>>>>>>>> {
>>>>>>>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
>>>>>>>> goto dereg;
>>>>>>>> }
>>>>>>>>
>>>>>>>> + rc = device_create_file(test_fw_misc_device.this_device,
>>>>>>>> + &dev_attr_trigger_ufw);
>>>>>>>> + if (rc) {
>>>>>>>> + pr_err("could not create sysfs interface: %d\n", rc);
>>>>>>>> + goto dereg;
>>>>>>>> + }
>>>>>>>> pr_warn("interface ready\n");
>>>>>>>>
>>>>>>>> return 0;
>>>>>>>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
>>>>>>>> {
>>>>>>>> release_firmware(test_firmware);
>>>>>>>> device_remove_file(test_fw_misc_device.this_device,
>>>>>>>> - &dev_attr_trigger_request);
>>>>>>>> + &dev_attr_trigger_request);
>>>>>>>> + device_remove_file(test_fw_misc_device.this_device,
>>>>>>>> + &dev_attr_trigger_ufw);
>>>>>>>> misc_deregister(&test_fw_misc_device);
>>>>>>>> pr_warn("removed interface\n");
>>>>>>>> }
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> ----------------------------8<--------------------------------------------
>>>>>>>>
>>>>>>>> Thanks and regards,
>>>>>>>> Chandrasekhar L.
>>>>>>>> --
>>>>>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>>>>>> member of
>>>>>>>> Code Aurora Forum,
>>>>>>>> a Linux Foundation Collaborative Project.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
[toc] | [prev] | [next] | [standalone]
| From | Ming Lei <ming.lei@canonical.com> |
|---|---|
| Date | 2016-03-16 11:30 +0100 |
| Message-ID | <rdgSe-7Ep-27@gated-at.bofh.it> |
| In reply to | #1358779 |
On Wed, 16 Mar 2016 15:21:24 +0530
Chandra Sekhar Lingutla <clingutla@codeaurora.org> wrote:
> Hi Ming,
>
> On 03/16/2016 02:34 PM, Chandra Sekhar Lingutla wrote:
> > On 03/16/2016 02:28 PM, Ming Lei wrote:
> >> On Wed, Mar 16, 2016 at 4:48 PM, Chandra Sekhar Lingutla
> >> <clingutla@codeaurora.org> wrote:
> >>> On 03/16/2016 02:12 PM, Ming Lei wrote:
> >>>>
> >>>> On Wed, Mar 16, 2016 at 3:02 PM, Chandra Sekhar Lingutla
> >>>> <clingutla@codeaurora.org> wrote:
> >>>>>
> >>>>> Hi Ming,
> >>>>>
> >>>>>
> >>>>> On 03/16/2016 07:36 AM, Ming Lei wrote:
> >>>>>>
> >>>>>>
> >>>>>> On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@canonical.com>
> >>>>>> wrote:
> >>>>>>>
> >>>>>>>
> >>>>>>> Hi,
> >>>>>>>
> >>>>>>> On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Hello,
> >>>>>>>>
> >>>>>>>> I see possible race in _request_firmware_load function, on which I
> >>>>>>>> wanted to
> >>>>>>>> take your opinion.
> >>>>>>>>
> >>>>>>>> When system is going to low power mode, device_cache_fw_images() is
> >>>>>>>> called
> >>>>>>>> from pm notifier which schedules asynchronous workers to cache devices
> >>>>>>>> firmware.
> >>>>>>>> If more than 2 async requests falls under user helper mode, then there
> >>>>>>>> is a
> >>>>>>>> use after free of "firmware" directory kobject.
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> If two requests are for getting same firmware image, only one can be
> >>>>>>> sent
> >>>>>>> out and be completed with user helper, please see
> >>>>>>> fw_lookup_and_allocate_buf(),
> >>>>>>> so the race shouldn't have been triggered in this case.
> >>>>>>>
> >>>>>>> So I guess your test must be involved with at least two different
> >>>>>>> requests.
> >>>>>>>
> >>>>>>>>
> >>>>>>>> The race will hit, when one asynchronous worker calls device_del()
> >>>>>>>> while
> >>>>>>>> other asynchronous worker calls get_device_parent() in
> >>>>>>>> _request_firmware_load().
> >>>>>>>> After loading firmware, first worker calls device_del(), and
> >>>>>>>> "firmware"
> >>>>>>>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put()
> >>>>>>>> with
> >>>>>>>> gdp_mutex lock held.
> >>>>>>>> Meanwhile, second async worker calls device_add(), and
> >>>>>>>> get_device_parent()
> >>>>>>>> is still able to find the firmware directory kobject in ksets after
> >>>>>>>> getting
> >>>>>>>> gdp_mutex.
> >>>>>>>> This kobject gets added as parent to the second device kobject.
> >>>>>>>> By the time of accessing the parent kobject, its ref count was 0 and
> >>>>>>>> prints
> >>>>>>>> below warning stack followed by crash.
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> The trick here is just that we don't use 'struct device' in
> >>>>>>> device_cache_fw_images(),
> >>>>>>> then the firmware device's parent is null during calling device_add()
> >>>>>>> from
> >>>>>>> _request_firmware_load(), but this should be allowed by driver core.
> >>>>>>>
> >>>>>>> From firmware class view, both device_add()/device_del() is run with
> >>>>>>> pair,
> >>>>>>> and driver core still complains during get_device_parent(), so
> >>>>>>> something
> >>>>>>> inside driver core should be be wrong, IMO.
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> Thinking about the issue further, I believe it is a false positive which
> >>>>>> is
> >>>>>> caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
> >>>>>>
> >>>>>> 1) device_add() path
> >>>>>>
> >>>>>> get_device_parent()
> >>>>>> ......
> >>>>>> mutex_lock(&gdp_mutex);
> >>>>>>
> >>>>>> /* find our class-directory at the parent and
> >>>>>> reference
> >>>>>> it */
> >>>>>> spin_lock(&dev->class->p->glue_dirs.list_lock);
> >>>>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list,
> >>>>>> entry)
> >>>>>> if (k->parent == parent_kobj) {
> >>>>>> kobj = kobject_get(k);
> >>>>>> break;
> >>>>>> }
> >>>>>> spin_unlock(&dev->class->p->glue_dirs.list_lock);
> >>>>>> if (kobj) {
> >>>>>> mutex_unlock(&gdp_mutex);
> >>>>>> return kobj;
> >>>>>> }
> >>>>>> k = class_dir_create_and_add(dev->class, parent_kobj);
> >>>>>> mutex_unlock(&gdp_mutex);
> >>>>>> ......
> >>>>>>
> >>>>>> 2) device_del() path
> >>>>>>
> >>>>>> cleanup_device_parent()
> >>>>>> ->cleanup_glue_dir()
> >>>>>> ->mutex_lock(&gdp_mutex);
> >>>>>> ->kobject_put(glue_dir);
> >>>>>> ->kobject_cleanup()
> >>>>>> ->kobject_del()
> >>>>>> ->kobj_kset_leave()
> >>>>>> ->mutex_unlock(&gdp_mutex);
> >>>>>>
> >>>>>> So gdp_mutex is held wrt. both looking up/adding the parent kobject
> >>>>>> and removing the parent kobject. Actually with this lock, both glur_dir
> >>>>>> kobject's referece counting and joining/leaving kset are run atomically.
> >>>>>>
> >>>>>> The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
> >>>>>> which causes kobject_cleanup() to be run in workqueue context and the
> >>>>>> lock of gdp_mutex can't be hold in that situation anymore. That is the
> >>>>>> root
> >>>>>> cause for your race.
> >>>>>>
> >>>>>> That also said DEBUG_KOBJECT_RELEASE might cause trouble in
> >>>>>> some situations.
> >>>>>>
> >>>>>> Thanks,
> >>>>>> Ming
> >>>>>>
> >>>>> I agree that, CONFIG_DEBUG_KOBJECT_RELEASE can cause the race, as it
> >>>>> delays
> >>>>> call to kobject_cleanup() which deletes kobj entry in glue_dir list.
> >>>>>
> >>>>> I see the race even after disabling CONFIG_DEBUG_KOBJECT_RELEASE.
> >>>>>
> >>>>> The race is between kobject_put() and kobject_get() for the "firmware"
> >>>>> directory.
> >>>>>
> >>>>> In device_del() path, I see the race after the call of
> >>>>> cleanup_device_parent().
> >>>>> cleanup_device_parent() calls kobject_put(glue_dir) with gdp_mutex lock
> >>>>> holding,
> >>>>> So ideally, to call kobject_put/kobject_get(glue_dir) we need to acquire
> >>>>> gdp_mutex.
> >>>>>
> >>>>> but kobject_del(kobj) will not hold the gdp_mutex lock while calling
> >>>>> kobject_put(kobj->parent).
> >>>>>
> >>>>> Here is the race:
> >>>>>
> >>>>> Consider 2 async works calls request_firmware() for 2 different binaries
> >>>>> (fw1.bin, fw2.bin)
> >>>>> Async work1 got scheduled first, and it falls in user helper mode so it
> >>>>> creates "firmware" dir
> >>>>> and then creates "fw1.bin" directory to load data from user.
> >>>>> After load completion or timeout, it starts cleanup dir's, meantime async
> >>>>> work2 got scheduled and
> >>>>> it also falls in user helper mode, and story starts here:
> >>>>>
> >>>>> PATH1 req fw for "fw1.bin"
> >>>>> PATH2
> >>>>> req fw for "fw2.bin"
> >>>>> _request_firmware_load()
> >>>>> device_del(dev1)
> >>>>>
> >>>>> ->cleanup_device_parent()
> >>>>>
> >>>>> mutex_lock(&gdp_mutex);
> >>>>>
> >>>>> _request_firmware_load("fw2.bin")
> >>>>> kobject_put(kobj->parent); --> firmware ref ->1
> >>>>> ->device_add(dev2)
> >>>>> mutex_unlock(&gdp_mutex);
> >>>>> ->get_device_parent()
> >>>>> ->kobject_del()
> >>>>> mutex_lock(&gdp_mutex)
> >>>>> kobj_kset_leave(kobj); -->del "fw1.bin" kobj in kset
> >>>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
> >>>>> kobject_put(kobj->parent); /* No lock :)*/
> >>>>> if (k->parent == parent_kobj) {
> >>>>>
> >>>>> ->kref_put() --> firmware ref ->0
> >>>>> kobj = kobject_get(k); -> k is "firmware"
> >>>>> dir
> >>>>> ->kboject_release()
> >>>>> break;
> >>>>>
> >>>>> ->kobject_del()
> >>>>> }
> >>>>>
> >>>>> /*here deletes firmware entry in kset*/
> >>>>> mutex_unlock(&gdp_mutex)
> >>>>>
> >>>>> ->dev2->kobj.parent = kobj -> kobj is released already
> >>>>>
> >>>>>
> >>>>>
> >>>>> PATH 1 is started removing the kobject of "fw1.bin" and its parent
> >>>>> "firmware"
> >>>>> .
> >>>>> cleanup_device_parent(dev1) makes firmware ref count to 1, by calling
> >>>>> kobject_put(firmware) with gdp_mutex held.
> >>>>>
> >>>>> and kobject_del(dev1->kobj) will again calls kobject_put(kobj->parent)
> >>>>> without holding gdp_mutex.
> >>>>>
> >>>>> In PATH2, glue_dir is able to find "firmware" kobj, as firmware dir kobj
> >>>>> is
> >>>>> deleted from the glue_dir list at kboject_release().
> >>>>> and it calls kobject_get(firmware), by the time PATH1 calls
> >>>>> kobject_release(firmware).
> >>>>>
> >>>>> So PATH2 got reference of freed firmware kobj and added as parent to
> >>>>> "fw2.bin" kobj.
> >>>>>
> >>>>> I think, here is possible fix for this race:
> >>>>>
> >>>>> ------------------------8<-------------------------------------
> >>>>> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
> >>>>>
> >>>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
> >>>>> index 5d8b713..47bc082 100644
> >>>>> --- a/drivers/base/core.c
> >>>>> +++ b/drivers/base/core.c
> >>>>> @@ -1224,7 +1224,13 @@ void device_del(struct device *dev)
> >>>>> BUS_NOTIFY_REMOVED_DEVICE,
> >>>>> dev);
> >>>>> kobject_uevent(&dev->kobj, KOBJ_REMOVE);
> >>>>> cleanup_device_parent(dev);
> >>>>> - kobject_del(&dev->kobj);
> >>>>> +
> >>>>> + if (dev->kobj.parent->kset == &dev->class->p->glue_dirs) {
> >>>>> + mutex_lock(&gdp_mutex);
> >>>>> + kobject_del(&dev->kobj);
> >>>>> + mutex_unlock(&gdp_mutex);
> >>>>> + } else
> >>>>> + kobject_del(&dev->kobj);
> >>>>> put_device(parent);
> >>>>> }
> >>>>> EXPORT_SYMBOL_GPL(device_del);
> >>>>>
> >>>>> --------------------------->8-----------------------------------
> >>>>
> >>>>
> >>>> OK, one simpler way is to move cleanup_device_parent(dev)
> >>>> after kobject_del(&dev->kobj), which looks more clean too.
> >>>>
> >>> No, We can't move that, bcz kobject_del(&dev->kobj) will clear the parent.
> >>
> >> Yeah, but I think it is better to do that and just call
> >> cleanup_glue_dir() directly
> >> because cleanup_device_parent() should have released the glue_dir.
> >>
> Sorry, i am not able understand correctly, If we reorder kobje_del and cleanup_device_parent(),
> kobject_del() clears kobj->parent, and cleanup_device_parent() gets glue_dir with dev->kobj->parent(),
> cleanup_glue_dir() returns without calling kobject_put() as glue_dir is NULL, so firmware dir becomes dangling kobj.
> Am I missing something here?
I mean something like below, and what do you think about it?
---
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 0a8bdad..3f2e1f8 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -836,11 +836,31 @@ static struct kobject *get_device_parent(struct device *dev,
return NULL;
}
+static inline bool live_in_glue_dir(struct kobject *kobj,
+ struct device *dev)
+{
+ if (!kobj || !dev->class ||
+ kobj->kset != &dev->class->p->glue_dirs)
+ return true;
+ return false;
+}
+
+static inline struct kobject *get_glue_dir(struct device *dev)
+{
+ if (live_in_glue_dir(&dev->kobj, dev))
+ return dev->kobj.parent;
+ return NULL;
+}
+
+/*
+ * make sure cleaning up dir as the last step, we need to make
+ * sure .release handler of kobject is run with holding the
+ * global lock
+ */
static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
{
/* see if we live in a "glue" directory */
- if (!glue_dir || !dev->class ||
- glue_dir->kset != &dev->class->p->glue_dirs)
+ if (!live_in_glue_dir(glue_dir, dev))
return;
mutex_lock(&gdp_mutex);
@@ -848,11 +868,6 @@ static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
mutex_unlock(&gdp_mutex);
}
-static void cleanup_device_parent(struct device *dev)
-{
- cleanup_glue_dir(dev, dev->kobj.parent);
-}
-
static int device_add_class_symlinks(struct device *dev)
{
struct device_node *of_node = dev_of_node(dev);
@@ -1028,6 +1043,7 @@ int device_add(struct device *dev)
struct kobject *kobj;
struct class_interface *class_intf;
int error = -EINVAL;
+ struct kobject *glue_dir = NULL;
dev = get_device(dev);
if (!dev)
@@ -1072,8 +1088,10 @@ int device_add(struct device *dev)
/* first, register with generic layer. */
/* we require the name to be set before, and pass NULL */
error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
- if (error)
+ if (error) {
+ glue_dir = get_glue_dir(dev);
goto Error;
+ }
/* notify platform of device entry */
if (platform_notify)
@@ -1154,9 +1172,10 @@ done:
device_remove_file(dev, &dev_attr_uevent);
attrError:
kobject_uevent(&dev->kobj, KOBJ_REMOVE);
+ glue_dir = get_glue_dir(dev);
kobject_del(&dev->kobj);
Error:
- cleanup_device_parent(dev);
+ cleanup_glue_dir(dev, glue_dir);
put_device(parent);
name_error:
kfree(dev->p);
@@ -1232,6 +1251,7 @@ EXPORT_SYMBOL_GPL(put_device);
void device_del(struct device *dev)
{
struct device *parent = dev->parent;
+ struct kobject *glue_dir = NULL;
struct class_interface *class_intf;
/* Notify clients of device removal. This call must come
@@ -1276,8 +1296,9 @@ void device_del(struct device *dev)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_REMOVED_DEVICE, dev);
kobject_uevent(&dev->kobj, KOBJ_REMOVE);
- cleanup_device_parent(dev);
+ glue_dir = get_glue_dir(dev);
kobject_del(&dev->kobj);
+ cleanup_glue_dir(dev, glue_dir);
put_device(parent);
}
EXPORT_SYMBOL_GPL(device_del);
>
> >> BTW, failure path of device_add() has been broken already.
> >>
> > Yah, forgot to mention that. we need to reorder like above fix, can we?.
> >
> >>>
> >>>
> >>>>>
> >>>>>
> >>>>>>>
> >>>>>>>>
> >>>>>>>> [21147.455038] ------------[ cut here ]------------
> >>>>>>>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
> >>>>>>>> kobject_get+0x50/0x68()
> >>>>>>>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
> >>>>>>>> qcrypto_module(O)
> >>>>>>>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
> >>>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
> >>>>>>>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
> >>>>>>>> [21147.481296] Call trace:
> >>>>>>>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
> >>>>>>>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
> >>>>>>>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
> >>>>>>>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
> >>>>>>>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
> >>>>>>>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
> >>>>>>>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
> >>>>>>>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
> >>>>>>>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
> >>>>>>>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
> >>>>>>>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
> >>>>>>>> [21147.481490] [<ffffffc00061c65c>]
> >>>>>>>> __async_dev_cache_fw_image+0x14/0x54
> >>>>>>>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
> >>>>>>>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
> >>>>>>>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
> >>>>>>>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
> >>>>>>>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
> >>>>>>>>
> >>>>>>>> [21147.486436] Unable to handle kernel paging request at virtual
> >>>>>>>> address
> >>>>>>>> 0x6b6b6b6b6b6b6bcb
> >>>>>>>> [21147.493816] pgd = ffffffc0a982d000
> >>>>>>>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
> >>>>>>>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> >>>>>>>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
> >>>>>>>> qcrypto_module(O)
> >>>>>>>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
> >>>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
> >>>>>>>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
> >>>>>>>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
> >>>>>>>> ffffffc007880000
> >>>>>>>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
> >>>>>>>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
> >>>>>>>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>]
> >>>>>>>> pstate:
> >>>>>>>> 80000145
> >>>>>>>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
> >>>>>>>> 0xffffffc007880058)
> >>>>>>>> [21148.003673] Call trace:
> >>>>>>>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
> >>>>>>>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
> >>>>>>>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
> >>>>>>>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
> >>>>>>>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
> >>>>>>>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
> >>>>>>>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
> >>>>>>>> [21148.044822] [<ffffffc00061c65c>]
> >>>>>>>> __async_dev_cache_fw_image+0x14/0x54
> >>>>>>>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
> >>>>>>>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
> >>>>>>>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
> >>>>>>>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
> >>>>>>>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
> >>>>>>>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
> >>>>>>>>
> >>>>>>>> Below is the callstack where the parent is freed from the slub_debug
> >>>>>>>> info.
> >>>>>>>> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
> >>>>>>>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
> >>>>>>>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
> >>>>>>>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
> >>>>>>>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
> >>>>>>>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
> >>>>>>>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
> >>>>>>>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
> >>>>>>>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
> >>>>>>>> 0xFFFFFFC00061C524
> >>>>>>>> \\vmlinux\firmware_class\_request_firmware\out+0x71C
> >>>>>>>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
> >>>>>>>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
> >>>>>>>> 0xFFFFFFC00061C65C
> >>>>>>>> \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
> >>>>>>>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
> >>>>>>>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
> >>>>>>>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
> >>>>>>>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
> >>>>>>>>
> >>>>>>>> For similar type of issue, I see there is an existing fix: "sysfs:
> >>>>>>>> driver
> >>>>>>>> core: Fix glue dir race condition by gdp_mutex".
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
> >>>>>>>>
> >>>>>>>> Still I am able to reproduce the issue. I have verified this race on
> >>>>>>>> kernels: 3.10, 3.18 and 4.4.
> >>>>>>>>
> >>>>>>>> I followed below procedure to reproduce the issue:
> >>>>>>>> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
> >>>>>>>> 2. Use test_firmware, modified the test for async calls
> >>>>>>>> 3. Replace WARN_ON with BUG_ON in kref_get().
> >>>>>>>> I ran below script from shell:
> >>>>>>>> count=0
> >>>>>>>> while [ 1 ]
> >>>>>>>> do
> >>>>>>>> echo 3 >
> >>>>>>>> /sys/devices/virtual/misc/test_firmware/trigger_ufw
> >>>>>>>> if [ $? -ne 0 ]; then
> >>>>>>>> print "Exiting.. "
> >>>>>>>> exit 1
> >>>>>>>> fi
> >>>>>>>> count=$(($count +1))
> >>>>>>>> echo "count $count"
> >>>>>>>> done
> >>>>>>>>
> >>>>>>>> With below patch, I could reproduce the issue in the 2nd iteration.
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> I will run your test script to see if there is new findings.
> >>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> -------------------------8<----------------------------------------------
> >>>>>>>>
> >>>>>>>> To reproduce the race condition, use firmware test and
> >>>>>>>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
> >>>>>>>> releases. So that we can catch the bug easily.
> >>>>>>>>
> >>>>>>>> Enabled below flags in kernel config file:
> >>>>>>>>
> >>>>>>>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
> >>>>>>>> +CONFIG_TEST_FIRMWARE=y
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> Looks I can't reproduce the issue with your approach.
> >>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
> >>>>>>>> index 484604d..727fb24 100644
> >>>>>>>> --- a/include/linux/kref.h
> >>>>>>>> +++ b/include/linux/kref.h
> >>>>>>>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
> >>>>>>>> * condition when this kref is freeing by some other thread
> >>>>>>>> right
> >>>>>>>> now.
> >>>>>>>> * In this case one should use kref_get_unless_zero()
> >>>>>>>> */
> >>>>>>>> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
> >>>>>>>> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
> >>>>>>>> }
> >>>>>>>>
> >>>>>>>> /**
> >>>>>>>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
> >>>>>>>> old mode 100644
> >>>>>>>> new mode 100755
> >>>>>>>> index 86374c1..14c9598
> >>>>>>>> --- a/lib/test_firmware.c
> >>>>>>>> +++ b/lib/test_firmware.c
> >>>>>>>> @@ -18,6 +18,7 @@
> >>>>>>>> #include <linux/miscdevice.h>
> >>>>>>>> #include <linux/slab.h>
> >>>>>>>> #include <linux/uaccess.h>
> >>>>>>>> +#include <linux/async.h>
> >>>>>>>>
> >>>>>>>> +
> >>>>>>>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
> >>>>>>>> +
> >>>>>>>> +static void __async_ufw_work(void *name,
> >>>>>>>> + async_cookie_t cookie)
> >>>>>>>> +{
> >>>>>>>> + const struct firmware *fw;
> >>>>>>>> + const char *fw_name = name;
> >>>>>>>> + int ret;
> >>>>>>>> +
> >>>>>>>> + pr_err("requesting %s\n", fw_name);
> >>>>>>>> +
> >>>>>>>> + ret = request_firmware(&fw, fw_name, NULL);
> >>>>>>>> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
> >>>>>>>> + if (!ret)
> >>>>>>>> + kfree(fw);
> >>>>>>>> +
> >>>>>>>> +}
> >>>>>>>> +
> >>>>>>>> +static char *name[] = { "fw1.bin", "fw2.bin"};
> >>>>>>>> +
> >>>>>>>> +static ssize_t trigger_ufw_store(struct device *dev,
> >>>>>>>> + struct device_attribute *attr,
> >>>>>>>> + const char *buf, size_t count)
> >>>>>>>> +{
> >>>>>>>> + int rc, i, c=0;
> >>>>>>>> + u32 start;
> >>>>>>>> + char *fw_name;
> >>>>>>>> +
> >>>>>>>> + rc = kstrtou32(buf, 0, &start);
> >>>>>>>> + if (rc){
> >>>>>>>> + pr_err("Invalid option\n");
> >>>>>>>> + return rc;
> >>>>>>>> + }
> >>>>>>>> + pr_err(" no of iterations %d\n", start);
> >>>>>>>> +
> >>>>>>>> + for (i=0; i< start; i++)
> >>>>>>>> + {
> >>>>>>>> + if (c >= 2)
> >>>>>>>> + c = 0;
> >>>>>>>> + fw_name = name[c++];
> >>>>>>>> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
> >>>>>>>> &ufw_domain);
> >>>>>>>> + }
> >>>>>>>> + async_synchronize_full_domain(&ufw_domain);
> >>>>>>>> + return count;
> >>>>>>>> +}
> >>>>>>>>
> >>>>>>>> static DEVICE_ATTR_WO(trigger_request);
> >>>>>>>> +static DEVICE_ATTR_WO(trigger_ufw);
> >>>>>>>>
> >>>>>>>> static int __init test_firmware_init(void)
> >>>>>>>> {
> >>>>>>>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
> >>>>>>>> goto dereg;
> >>>>>>>> }
> >>>>>>>>
> >>>>>>>> + rc = device_create_file(test_fw_misc_device.this_device,
> >>>>>>>> + &dev_attr_trigger_ufw);
> >>>>>>>> + if (rc) {
> >>>>>>>> + pr_err("could not create sysfs interface: %d\n", rc);
> >>>>>>>> + goto dereg;
> >>>>>>>> + }
> >>>>>>>> pr_warn("interface ready\n");
> >>>>>>>>
> >>>>>>>> return 0;
> >>>>>>>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
> >>>>>>>> {
> >>>>>>>> release_firmware(test_firmware);
> >>>>>>>> device_remove_file(test_fw_misc_device.this_device,
> >>>>>>>> - &dev_attr_trigger_request);
> >>>>>>>> + &dev_attr_trigger_request);
> >>>>>>>> + device_remove_file(test_fw_misc_device.this_device,
> >>>>>>>> + &dev_attr_trigger_ufw);
> >>>>>>>> misc_deregister(&test_fw_misc_device);
> >>>>>>>> pr_warn("removed interface\n");
> >>>>>>>> }
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> ----------------------------8<--------------------------------------------
> >>>>>>>>
> >>>>>>>> Thanks and regards,
> >>>>>>>> Chandrasekhar L.
> >>>>>>>> --
> >>>>>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
> >>>>>>>> member of
> >>>>>>>> Code Aurora Forum,
> >>>>>>>> a Linux Foundation Collaborative Project.
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
[toc] | [prev] | [next] | [standalone]
| From | Chandra Sekhar Lingutla <clingutla@codeaurora.org> |
|---|---|
| Date | 2016-03-17 07:00 +0100 |
| Message-ID | <rdz8u-37q-1@gated-at.bofh.it> |
| In reply to | #1358805 |
Hi Ming,
On 03/16/2016 03:55 PM, Ming Lei wrote:
> On Wed, 16 Mar 2016 15:21:24 +0530
> Chandra Sekhar Lingutla <clingutla@codeaurora.org> wrote:
>
>> Hi Ming,
>>
>> On 03/16/2016 02:34 PM, Chandra Sekhar Lingutla wrote:
>>> On 03/16/2016 02:28 PM, Ming Lei wrote:
>>>> On Wed, Mar 16, 2016 at 4:48 PM, Chandra Sekhar Lingutla
>>>> <clingutla@codeaurora.org> wrote:
>>>>> On 03/16/2016 02:12 PM, Ming Lei wrote:
>>>>>>
>>>>>> On Wed, Mar 16, 2016 at 3:02 PM, Chandra Sekhar Lingutla
>>>>>> <clingutla@codeaurora.org> wrote:
>>>>>>>
>>>>>>> Hi Ming,
>>>>>>>
>>>>>>>
>>>>>>> On 03/16/2016 07:36 AM, Ming Lei wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@canonical.com>
>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Hi,
>>>>>>>>>
>>>>>>>>> On Mon, Mar 14, 2016 at 8:00 PM, <clingutla@codeaurora.org> wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Hello,
>>>>>>>>>>
>>>>>>>>>> I see possible race in _request_firmware_load function, on which I
>>>>>>>>>> wanted to
>>>>>>>>>> take your opinion.
>>>>>>>>>>
>>>>>>>>>> When system is going to low power mode, device_cache_fw_images() is
>>>>>>>>>> called
>>>>>>>>>> from pm notifier which schedules asynchronous workers to cache devices
>>>>>>>>>> firmware.
>>>>>>>>>> If more than 2 async requests falls under user helper mode, then there
>>>>>>>>>> is a
>>>>>>>>>> use after free of "firmware" directory kobject.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> If two requests are for getting same firmware image, only one can be
>>>>>>>>> sent
>>>>>>>>> out and be completed with user helper, please see
>>>>>>>>> fw_lookup_and_allocate_buf(),
>>>>>>>>> so the race shouldn't have been triggered in this case.
>>>>>>>>>
>>>>>>>>> So I guess your test must be involved with at least two different
>>>>>>>>> requests.
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> The race will hit, when one asynchronous worker calls device_del()
>>>>>>>>>> while
>>>>>>>>>> other asynchronous worker calls get_device_parent() in
>>>>>>>>>> _request_firmware_load().
>>>>>>>>>> After loading firmware, first worker calls device_del(), and
>>>>>>>>>> "firmware"
>>>>>>>>>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put()
>>>>>>>>>> with
>>>>>>>>>> gdp_mutex lock held.
>>>>>>>>>> Meanwhile, second async worker calls device_add(), and
>>>>>>>>>> get_device_parent()
>>>>>>>>>> is still able to find the firmware directory kobject in ksets after
>>>>>>>>>> getting
>>>>>>>>>> gdp_mutex.
>>>>>>>>>> This kobject gets added as parent to the second device kobject.
>>>>>>>>>> By the time of accessing the parent kobject, its ref count was 0 and
>>>>>>>>>> prints
>>>>>>>>>> below warning stack followed by crash.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> The trick here is just that we don't use 'struct device' in
>>>>>>>>> device_cache_fw_images(),
>>>>>>>>> then the firmware device's parent is null during calling device_add()
>>>>>>>>> from
>>>>>>>>> _request_firmware_load(), but this should be allowed by driver core.
>>>>>>>>>
>>>>>>>>> From firmware class view, both device_add()/device_del() is run with
>>>>>>>>> pair,
>>>>>>>>> and driver core still complains during get_device_parent(), so
>>>>>>>>> something
>>>>>>>>> inside driver core should be be wrong, IMO.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Thinking about the issue further, I believe it is a false positive which
>>>>>>>> is
>>>>>>>> caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
>>>>>>>>
>>>>>>>> 1) device_add() path
>>>>>>>>
>>>>>>>> get_device_parent()
>>>>>>>> ......
>>>>>>>> mutex_lock(&gdp_mutex);
>>>>>>>>
>>>>>>>> /* find our class-directory at the parent and
>>>>>>>> reference
>>>>>>>> it */
>>>>>>>> spin_lock(&dev->class->p->glue_dirs.list_lock);
>>>>>>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list,
>>>>>>>> entry)
>>>>>>>> if (k->parent == parent_kobj) {
>>>>>>>> kobj = kobject_get(k);
>>>>>>>> break;
>>>>>>>> }
>>>>>>>> spin_unlock(&dev->class->p->glue_dirs.list_lock);
>>>>>>>> if (kobj) {
>>>>>>>> mutex_unlock(&gdp_mutex);
>>>>>>>> return kobj;
>>>>>>>> }
>>>>>>>> k = class_dir_create_and_add(dev->class, parent_kobj);
>>>>>>>> mutex_unlock(&gdp_mutex);
>>>>>>>> ......
>>>>>>>>
>>>>>>>> 2) device_del() path
>>>>>>>>
>>>>>>>> cleanup_device_parent()
>>>>>>>> ->cleanup_glue_dir()
>>>>>>>> ->mutex_lock(&gdp_mutex);
>>>>>>>> ->kobject_put(glue_dir);
>>>>>>>> ->kobject_cleanup()
>>>>>>>> ->kobject_del()
>>>>>>>> ->kobj_kset_leave()
>>>>>>>> ->mutex_unlock(&gdp_mutex);
>>>>>>>>
>>>>>>>> So gdp_mutex is held wrt. both looking up/adding the parent kobject
>>>>>>>> and removing the parent kobject. Actually with this lock, both glur_dir
>>>>>>>> kobject's referece counting and joining/leaving kset are run atomically.
>>>>>>>>
>>>>>>>> The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
>>>>>>>> which causes kobject_cleanup() to be run in workqueue context and the
>>>>>>>> lock of gdp_mutex can't be hold in that situation anymore. That is the
>>>>>>>> root
>>>>>>>> cause for your race.
>>>>>>>>
>>>>>>>> That also said DEBUG_KOBJECT_RELEASE might cause trouble in
>>>>>>>> some situations.
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Ming
>>>>>>>>
>>>>>>> I agree that, CONFIG_DEBUG_KOBJECT_RELEASE can cause the race, as it
>>>>>>> delays
>>>>>>> call to kobject_cleanup() which deletes kobj entry in glue_dir list.
>>>>>>>
>>>>>>> I see the race even after disabling CONFIG_DEBUG_KOBJECT_RELEASE.
>>>>>>>
>>>>>>> The race is between kobject_put() and kobject_get() for the "firmware"
>>>>>>> directory.
>>>>>>>
>>>>>>> In device_del() path, I see the race after the call of
>>>>>>> cleanup_device_parent().
>>>>>>> cleanup_device_parent() calls kobject_put(glue_dir) with gdp_mutex lock
>>>>>>> holding,
>>>>>>> So ideally, to call kobject_put/kobject_get(glue_dir) we need to acquire
>>>>>>> gdp_mutex.
>>>>>>>
>>>>>>> but kobject_del(kobj) will not hold the gdp_mutex lock while calling
>>>>>>> kobject_put(kobj->parent).
>>>>>>>
>>>>>>> Here is the race:
>>>>>>>
>>>>>>> Consider 2 async works calls request_firmware() for 2 different binaries
>>>>>>> (fw1.bin, fw2.bin)
>>>>>>> Async work1 got scheduled first, and it falls in user helper mode so it
>>>>>>> creates "firmware" dir
>>>>>>> and then creates "fw1.bin" directory to load data from user.
>>>>>>> After load completion or timeout, it starts cleanup dir's, meantime async
>>>>>>> work2 got scheduled and
>>>>>>> it also falls in user helper mode, and story starts here:
>>>>>>>
>>>>>>> PATH1 req fw for "fw1.bin"
>>>>>>> PATH2
>>>>>>> req fw for "fw2.bin"
>>>>>>> _request_firmware_load()
>>>>>>> device_del(dev1)
>>>>>>>
>>>>>>> ->cleanup_device_parent()
>>>>>>>
>>>>>>> mutex_lock(&gdp_mutex);
>>>>>>>
>>>>>>> _request_firmware_load("fw2.bin")
>>>>>>> kobject_put(kobj->parent); --> firmware ref ->1
>>>>>>> ->device_add(dev2)
>>>>>>> mutex_unlock(&gdp_mutex);
>>>>>>> ->get_device_parent()
>>>>>>> ->kobject_del()
>>>>>>> mutex_lock(&gdp_mutex)
>>>>>>> kobj_kset_leave(kobj); -->del "fw1.bin" kobj in kset
>>>>>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
>>>>>>> kobject_put(kobj->parent); /* No lock :)*/
>>>>>>> if (k->parent == parent_kobj) {
>>>>>>>
>>>>>>> ->kref_put() --> firmware ref ->0
>>>>>>> kobj = kobject_get(k); -> k is "firmware"
>>>>>>> dir
>>>>>>> ->kboject_release()
>>>>>>> break;
>>>>>>>
>>>>>>> ->kobject_del()
>>>>>>> }
>>>>>>>
>>>>>>> /*here deletes firmware entry in kset*/
>>>>>>> mutex_unlock(&gdp_mutex)
>>>>>>>
>>>>>>> ->dev2->kobj.parent = kobj -> kobj is released already
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> PATH 1 is started removing the kobject of "fw1.bin" and its parent
>>>>>>> "firmware"
>>>>>>> .
>>>>>>> cleanup_device_parent(dev1) makes firmware ref count to 1, by calling
>>>>>>> kobject_put(firmware) with gdp_mutex held.
>>>>>>>
>>>>>>> and kobject_del(dev1->kobj) will again calls kobject_put(kobj->parent)
>>>>>>> without holding gdp_mutex.
>>>>>>>
>>>>>>> In PATH2, glue_dir is able to find "firmware" kobj, as firmware dir kobj
>>>>>>> is
>>>>>>> deleted from the glue_dir list at kboject_release().
>>>>>>> and it calls kobject_get(firmware), by the time PATH1 calls
>>>>>>> kobject_release(firmware).
>>>>>>>
>>>>>>> So PATH2 got reference of freed firmware kobj and added as parent to
>>>>>>> "fw2.bin" kobj.
>>>>>>>
>>>>>>> I think, here is possible fix for this race:
>>>>>>>
>>>>>>> ------------------------8<-------------------------------------
>>>>>>> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
>>>>>>>
>>>>>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>>>>>>> index 5d8b713..47bc082 100644
>>>>>>> --- a/drivers/base/core.c
>>>>>>> +++ b/drivers/base/core.c
>>>>>>> @@ -1224,7 +1224,13 @@ void device_del(struct device *dev)
>>>>>>> BUS_NOTIFY_REMOVED_DEVICE,
>>>>>>> dev);
>>>>>>> kobject_uevent(&dev->kobj, KOBJ_REMOVE);
>>>>>>> cleanup_device_parent(dev);
>>>>>>> - kobject_del(&dev->kobj);
>>>>>>> +
>>>>>>> + if (dev->kobj.parent->kset == &dev->class->p->glue_dirs) {
>>>>>>> + mutex_lock(&gdp_mutex);
>>>>>>> + kobject_del(&dev->kobj);
>>>>>>> + mutex_unlock(&gdp_mutex);
>>>>>>> + } else
>>>>>>> + kobject_del(&dev->kobj);
>>>>>>> put_device(parent);
>>>>>>> }
>>>>>>> EXPORT_SYMBOL_GPL(device_del);
>>>>>>>
>>>>>>> --------------------------->8-----------------------------------
>>>>>>
>>>>>>
>>>>>> OK, one simpler way is to move cleanup_device_parent(dev)
>>>>>> after kobject_del(&dev->kobj), which looks more clean too.
>>>>>>
>>>>> No, We can't move that, bcz kobject_del(&dev->kobj) will clear the parent.
>>>>
>>>> Yeah, but I think it is better to do that and just call
>>>> cleanup_glue_dir() directly
>>>> because cleanup_device_parent() should have released the glue_dir.
>>>>
>> Sorry, i am not able understand correctly, If we reorder kobje_del and cleanup_device_parent(),
>> kobject_del() clears kobj->parent, and cleanup_device_parent() gets glue_dir with dev->kobj->parent(),
>> cleanup_glue_dir() returns without calling kobject_put() as glue_dir is NULL, so firmware dir becomes dangling kobj.
>> Am I missing something here?
>
> I mean something like below, and what do you think about it?
>
> ---
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 0a8bdad..3f2e1f8 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -836,11 +836,31 @@ static struct kobject *get_device_parent(struct device *dev,
> return NULL;
> }
>
> +static inline bool live_in_glue_dir(struct kobject *kobj,
> + struct device *dev)
> +{
> + if (!kobj || !dev->class ||
> + kobj->kset != &dev->class->p->glue_dirs)
> + return true;
> + return false;
> +}
> +
> +static inline struct kobject *get_glue_dir(struct device *dev)
> +{
> + if (live_in_glue_dir(&dev->kobj, dev))
> + return dev->kobj.parent;
> + return NULL;
> +}
> +
> +/*
> + * make sure cleaning up dir as the last step, we need to make
> + * sure .release handler of kobject is run with holding the
> + * global lock
> + */
> static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
> {
> /* see if we live in a "glue" directory */
> - if (!glue_dir || !dev->class ||
> - glue_dir->kset != &dev->class->p->glue_dirs)
> + if (!live_in_glue_dir(glue_dir, dev))
> return;
>
> mutex_lock(&gdp_mutex);
> @@ -848,11 +868,6 @@ static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
> mutex_unlock(&gdp_mutex);
> }
>
> -static void cleanup_device_parent(struct device *dev)
> -{
> - cleanup_glue_dir(dev, dev->kobj.parent);
> -}
> -
> static int device_add_class_symlinks(struct device *dev)
> {
> struct device_node *of_node = dev_of_node(dev);
> @@ -1028,6 +1043,7 @@ int device_add(struct device *dev)
> struct kobject *kobj;
> struct class_interface *class_intf;
> int error = -EINVAL;
> + struct kobject *glue_dir = NULL;
>
> dev = get_device(dev);
> if (!dev)
> @@ -1072,8 +1088,10 @@ int device_add(struct device *dev)
> /* first, register with generic layer. */
> /* we require the name to be set before, and pass NULL */
> error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
> - if (error)
> + if (error) {
> + glue_dir = get_glue_dir(dev);
> goto Error;
> + }
>
> /* notify platform of device entry */
> if (platform_notify)
> @@ -1154,9 +1172,10 @@ done:
> device_remove_file(dev, &dev_attr_uevent);
> attrError:
> kobject_uevent(&dev->kobj, KOBJ_REMOVE);
> + glue_dir = get_glue_dir(dev);
> kobject_del(&dev->kobj);
> Error:
> - cleanup_device_parent(dev);
> + cleanup_glue_dir(dev, glue_dir);
> put_device(parent);
> name_error:
> kfree(dev->p);
> @@ -1232,6 +1251,7 @@ EXPORT_SYMBOL_GPL(put_device);
> void device_del(struct device *dev)
> {
> struct device *parent = dev->parent;
> + struct kobject *glue_dir = NULL;
> struct class_interface *class_intf;
>
> /* Notify clients of device removal. This call must come
> @@ -1276,8 +1296,9 @@ void device_del(struct device *dev)
> blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
> BUS_NOTIFY_REMOVED_DEVICE, dev);
> kobject_uevent(&dev->kobj, KOBJ_REMOVE);
> - cleanup_device_parent(dev);
> + glue_dir = get_glue_dir(dev);
> kobject_del(&dev->kobj);
> + cleanup_glue_dir(dev, glue_dir);
> put_device(parent);
> }
> EXPORT_SYMBOL_GPL(device_del);
>
>
This looks more clean to me.
>
>
>
>
>>
>>>> BTW, failure path of device_add() has been broken already.
>>>>
>>> Yah, forgot to mention that. we need to reorder like above fix, can we?.
>>>
>>>>>
>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> [21147.455038] ------------[ cut here ]------------
>>>>>>>>>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
>>>>>>>>>> kobject_get+0x50/0x68()
>>>>>>>>>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>>>>>>> qcrypto_module(O)
>>>>>>>>>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>>>>>>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
>>>>>>>>>> [21147.481296] Call trace:
>>>>>>>>>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
>>>>>>>>>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
>>>>>>>>>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
>>>>>>>>>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
>>>>>>>>>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
>>>>>>>>>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
>>>>>>>>>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
>>>>>>>>>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
>>>>>>>>>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>>>>>>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>>>>>>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>>>>>>> [21147.481490] [<ffffffc00061c65c>]
>>>>>>>>>> __async_dev_cache_fw_image+0x14/0x54
>>>>>>>>>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>>>>>>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>>>>>>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>>>>>>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>>>>>>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>>>>>>>>>>
>>>>>>>>>> [21147.486436] Unable to handle kernel paging request at virtual
>>>>>>>>>> address
>>>>>>>>>> 0x6b6b6b6b6b6b6bcb
>>>>>>>>>> [21147.493816] pgd = ffffffc0a982d000
>>>>>>>>>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
>>>>>>>>>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>>>>>>>>>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>>>>>>> qcrypto_module(O)
>>>>>>>>>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>>>>>>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
>>>>>>>>>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
>>>>>>>>>> ffffffc007880000
>>>>>>>>>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
>>>>>>>>>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
>>>>>>>>>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>]
>>>>>>>>>> pstate:
>>>>>>>>>> 80000145
>>>>>>>>>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
>>>>>>>>>> 0xffffffc007880058)
>>>>>>>>>> [21148.003673] Call trace:
>>>>>>>>>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
>>>>>>>>>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
>>>>>>>>>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
>>>>>>>>>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
>>>>>>>>>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>>>>>>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>>>>>>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>>>>>>> [21148.044822] [<ffffffc00061c65c>]
>>>>>>>>>> __async_dev_cache_fw_image+0x14/0x54
>>>>>>>>>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>>>>>>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>>>>>>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>>>>>>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>>>>>>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
>>>>>>>>>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>>>>>>>>>>
>>>>>>>>>> Below is the callstack where the parent is freed from the slub_debug
>>>>>>>>>> info.
>>>>>>>>>> 0xFFFFFFC000608D74 \\vmlinux\base/core\class_dir_release+0x0C
>>>>>>>>>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
>>>>>>>>>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
>>>>>>>>>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
>>>>>>>>>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
>>>>>>>>>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
>>>>>>>>>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
>>>>>>>>>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
>>>>>>>>>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
>>>>>>>>>> 0xFFFFFFC00061C524
>>>>>>>>>> \\vmlinux\firmware_class\_request_firmware\out+0x71C
>>>>>>>>>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
>>>>>>>>>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
>>>>>>>>>> 0xFFFFFFC00061C65C
>>>>>>>>>> \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
>>>>>>>>>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
>>>>>>>>>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
>>>>>>>>>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
>>>>>>>>>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>>>>>>>>>>
>>>>>>>>>> For similar type of issue, I see there is an existing fix: "sysfs:
>>>>>>>>>> driver
>>>>>>>>>> core: Fix glue dir race condition by gdp_mutex".
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>>>>>>>>>>
>>>>>>>>>> Still I am able to reproduce the issue. I have verified this race on
>>>>>>>>>> kernels: 3.10, 3.18 and 4.4.
>>>>>>>>>>
>>>>>>>>>> I followed below procedure to reproduce the issue:
>>>>>>>>>> 1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
>>>>>>>>>> 2. Use test_firmware, modified the test for async calls
>>>>>>>>>> 3. Replace WARN_ON with BUG_ON in kref_get().
>>>>>>>>>> I ran below script from shell:
>>>>>>>>>> count=0
>>>>>>>>>> while [ 1 ]
>>>>>>>>>> do
>>>>>>>>>> echo 3 >
>>>>>>>>>> /sys/devices/virtual/misc/test_firmware/trigger_ufw
>>>>>>>>>> if [ $? -ne 0 ]; then
>>>>>>>>>> print "Exiting.. "
>>>>>>>>>> exit 1
>>>>>>>>>> fi
>>>>>>>>>> count=$(($count +1))
>>>>>>>>>> echo "count $count"
>>>>>>>>>> done
>>>>>>>>>>
>>>>>>>>>> With below patch, I could reproduce the issue in the 2nd iteration.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I will run your test script to see if there is new findings.
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> -------------------------8<----------------------------------------------
>>>>>>>>>>
>>>>>>>>>> To reproduce the race condition, use firmware test and
>>>>>>>>>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
>>>>>>>>>> releases. So that we can catch the bug easily.
>>>>>>>>>>
>>>>>>>>>> Enabled below flags in kernel config file:
>>>>>>>>>>
>>>>>>>>>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
>>>>>>>>>> +CONFIG_TEST_FIRMWARE=y
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Looks I can't reproduce the issue with your approach.
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
>>>>>>>>>> index 484604d..727fb24 100644
>>>>>>>>>> --- a/include/linux/kref.h
>>>>>>>>>> +++ b/include/linux/kref.h
>>>>>>>>>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
>>>>>>>>>> * condition when this kref is freeing by some other thread
>>>>>>>>>> right
>>>>>>>>>> now.
>>>>>>>>>> * In this case one should use kref_get_unless_zero()
>>>>>>>>>> */
>>>>>>>>>> - WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
>>>>>>>>>> + BUG_ON(atomic_inc_return(&kref->refcount) < 2);
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> /**
>>>>>>>>>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>>>>>>>>>> old mode 100644
>>>>>>>>>> new mode 100755
>>>>>>>>>> index 86374c1..14c9598
>>>>>>>>>> --- a/lib/test_firmware.c
>>>>>>>>>> +++ b/lib/test_firmware.c
>>>>>>>>>> @@ -18,6 +18,7 @@
>>>>>>>>>> #include <linux/miscdevice.h>
>>>>>>>>>> #include <linux/slab.h>
>>>>>>>>>> #include <linux/uaccess.h>
>>>>>>>>>> +#include <linux/async.h>
>>>>>>>>>>
>>>>>>>>>> +
>>>>>>>>>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
>>>>>>>>>> +
>>>>>>>>>> +static void __async_ufw_work(void *name,
>>>>>>>>>> + async_cookie_t cookie)
>>>>>>>>>> +{
>>>>>>>>>> + const struct firmware *fw;
>>>>>>>>>> + const char *fw_name = name;
>>>>>>>>>> + int ret;
>>>>>>>>>> +
>>>>>>>>>> + pr_err("requesting %s\n", fw_name);
>>>>>>>>>> +
>>>>>>>>>> + ret = request_firmware(&fw, fw_name, NULL);
>>>>>>>>>> + pr_err("loaded: %zu\n", fw ? fw->size : 0);
>>>>>>>>>> + if (!ret)
>>>>>>>>>> + kfree(fw);
>>>>>>>>>> +
>>>>>>>>>> +}
>>>>>>>>>> +
>>>>>>>>>> +static char *name[] = { "fw1.bin", "fw2.bin"};
>>>>>>>>>> +
>>>>>>>>>> +static ssize_t trigger_ufw_store(struct device *dev,
>>>>>>>>>> + struct device_attribute *attr,
>>>>>>>>>> + const char *buf, size_t count)
>>>>>>>>>> +{
>>>>>>>>>> + int rc, i, c=0;
>>>>>>>>>> + u32 start;
>>>>>>>>>> + char *fw_name;
>>>>>>>>>> +
>>>>>>>>>> + rc = kstrtou32(buf, 0, &start);
>>>>>>>>>> + if (rc){
>>>>>>>>>> + pr_err("Invalid option\n");
>>>>>>>>>> + return rc;
>>>>>>>>>> + }
>>>>>>>>>> + pr_err(" no of iterations %d\n", start);
>>>>>>>>>> +
>>>>>>>>>> + for (i=0; i< start; i++)
>>>>>>>>>> + {
>>>>>>>>>> + if (c >= 2)
>>>>>>>>>> + c = 0;
>>>>>>>>>> + fw_name = name[c++];
>>>>>>>>>> + async_schedule_domain(__async_ufw_work, (void *)fw_name,
>>>>>>>>>> &ufw_domain);
>>>>>>>>>> + }
>>>>>>>>>> + async_synchronize_full_domain(&ufw_domain);
>>>>>>>>>> + return count;
>>>>>>>>>> +}
>>>>>>>>>>
>>>>>>>>>> static DEVICE_ATTR_WO(trigger_request);
>>>>>>>>>> +static DEVICE_ATTR_WO(trigger_ufw);
>>>>>>>>>>
>>>>>>>>>> static int __init test_firmware_init(void)
>>>>>>>>>> {
>>>>>>>>>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
>>>>>>>>>> goto dereg;
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> + rc = device_create_file(test_fw_misc_device.this_device,
>>>>>>>>>> + &dev_attr_trigger_ufw);
>>>>>>>>>> + if (rc) {
>>>>>>>>>> + pr_err("could not create sysfs interface: %d\n", rc);
>>>>>>>>>> + goto dereg;
>>>>>>>>>> + }
>>>>>>>>>> pr_warn("interface ready\n");
>>>>>>>>>>
>>>>>>>>>> return 0;
>>>>>>>>>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
>>>>>>>>>> {
>>>>>>>>>> release_firmware(test_firmware);
>>>>>>>>>> device_remove_file(test_fw_misc_device.this_device,
>>>>>>>>>> - &dev_attr_trigger_request);
>>>>>>>>>> + &dev_attr_trigger_request);
>>>>>>>>>> + device_remove_file(test_fw_misc_device.this_device,
>>>>>>>>>> + &dev_attr_trigger_ufw);
>>>>>>>>>> misc_deregister(&test_fw_misc_device);
>>>>>>>>>> pr_warn("removed interface\n");
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> ----------------------------8<--------------------------------------------
>>>>>>>>>>
>>>>>>>>>> Thanks and regards,
>>>>>>>>>> Chandrasekhar L.
>>>>>>>>>> --
>>>>>>>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>>>>>>>> member of
>>>>>>>>>> Code Aurora Forum,
>>>>>>>>>> a Linux Foundation Collaborative Project.
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
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