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Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning

Started byAlan Stern <stern@rowland.harvard.edu>
First post2016-03-01 17:10 +0100
Last post2016-03-02 09:40 +0100
Articles 5 — 3 participants

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  Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning Alan Stern <stern@rowland.harvard.edu> - 2016-03-01 17:10 +0100
    Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-02 07:40 +0100
      Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning Jiri Kosina <jikos@kernel.org> - 2016-03-02 09:40 +0100
        Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-02 10:20 +0100
      Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning Sedat Dilek <sedat.dilek@gmail.com> - 2016-03-02 09:40 +0100

#1346722 — Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning

FromAlan Stern <stern@rowland.harvard.edu>
Date2016-03-01 17:10 +0100
SubjectRe: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning
Message-ID<r7V22-2XK-25@gated-at.bofh.it>
On Tue, 1 Mar 2016, Sedat Dilek wrote:

> On Tue, Oct 13, 2015 at 2:57 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Sat, 3 Oct 2015 12:05:42 +0200
> > Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> >> So, at the beginning... dunno WTF is causing the problems - no
> >> workaround for CLANG.
> >
> > Probably need to compile with gcc and with clang and look at the binary
> > differences. Or at least what objdump shows.
> >
> 
> [ Hope to address this issue to the correct people - CCed some people
> I taped on their nerves ]
> 
> Not sure if I should open a new thread?
> Please, some clear statements on this.
> Thanks.
> 
> The issue is still visible and alive.

...

> [ FACT #3: TEST-CASE #2 ]
> 
> The most reliable test-case is to simply unplug my external Logitech
> USB mouse - saw this by accident.
> YES, it was so simple.
> 
> --- dmesg_4.5.0-rc6-2-llvmlinux-amd64.txt       2016-02-29
> 21:23:56.399691975 +0100
> +++ dmesg_4.5.0-rc6-2-llvmlinux-amd64_usbmouse-unplugged.txt
> 2016-02-29 21:28:14.401832240 +0100
> @@ -832,3 +832,75 @@
>  [   66.529779] PPP BSD Compression module registered
>  [   66.563013] PPP Deflate Compression module registered
>  [   66.978977] usb 2-1.5: USB disconnect, device number 4
> +[  321.937369] usb 2-1.4: USB disconnect, device number 3
> +[  321.950810] BUG: sleeping function called from invalid context at
> kernel/workqueue.c:2785
> +[  321.950816] in_atomic(): 0, irqs_disabled(): 1, pid: 44, name: kworker/2:1

> +[  321.950885] hardirqs last  enabled at (47769):
> [<ffffffff819426a2>] _raw_spin_unlock_irq+0x32/0x60
> +[  321.950889] hardirqs last disabled at (47770):
> [<ffffffff81115bdc>] del_timer_sync+0x3c/0x110
> +[  321.950894] softirqs last  enabled at (47112):
> [<ffffffff810871a2>] __do_softirq+0x5a2/0x610
> +[  321.950898] softirqs last disabled at (47097):
> [<ffffffff8108747c>] irq_exit+0x9c/0x120
> +[  321.950903] CPU: 2 PID: 44 Comm: kworker/2:1 Not tainted
> 4.5.0-rc6-2-llvmlinux-amd64 #1
> +[  321.950905] Hardware name: SAMSUNG ELECTRONICS CO., LTD.
> 530U3BI/530U4BI/530U4BH/530U3BI/530U4BI/530U4BH, BIOS 13XK 03/28/2013
> +[  321.950908] Workqueue: usb_hub_wq hub_event
> +[  321.950911]  ffff8800d3326948 0000000000000092 0000000000000000
> ffff8800d4347568
> +[  321.950915]  ffffffff814ba7d4 ffff8800d43474f8 ffff8800d4340cc0
> ffff8800d4347568
> +[  321.950919]  ffffffff810e28fd 0000000000000092 0000000000000096
> ffff8800d43475a8
> +[  321.950923] Call Trace:
> +[  321.950927]  [<ffffffff814ba7d4>] dump_stack+0xa4/0xf0
> +[  321.950931]  [<ffffffff810e28fd>] ? print_irqtrace_events+0xcd/0xe0
> +[  321.950936]  [<ffffffff810bf495>] ___might_sleep+0x295/0x2b0
> +[  321.950939]  [<ffffffff810bf18f>] __might_sleep+0x4f/0xc0
> +[  321.950943]  [<ffffffff810a12ef>] start_flush_work+0x2f/0x2a0
> +[  321.950946]  [<ffffffff810a129c>] flush_work+0x5c/0x80
> +[  321.950949]  [<ffffffff810a125a>] ? flush_work+0x1a/0x80
> +[  321.950953]  [<ffffffff810e247d>] ? trace_hardirqs_off+0xd/0x10
> +[  321.950956]  [<ffffffff810a032a>] ? try_to_grab_pending+0x4a/0x260
> +[  321.950960]  [<ffffffff810a1717>] __cancel_work_timer+0x197/0x290
> +[  321.950963]  [<ffffffff81115b8d>] ? try_to_del_timer_sync+0xad/0xc0
> +[  321.950966]  [<ffffffff810a1578>] cancel_work_sync+0x18/0x20

It's possible that this could be a compiler-related error connected 
with local_irq_save().  __cancel_work_timer() calls 

		ret = try_to_grab_pending(work, is_dwork, &flags);

and try_to_grab_pending() starts this way:

static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
			       unsigned long *flags)
{
	struct worker_pool *pool;
	struct pool_workqueue *pwq;

	local_irq_save(*flags);

Then later on, __cancel_work_timer() does

	local_irq_restore(flags);

Maybe CLANG doesn't like local_irq_save() applied to a pointer as 
opposed to a stack variable.

As a quick test, try applying the patch below.  (Note that there is a 
similar construction in kernel/signal.c.)

Alan Stern



Index: usb-4.4/kernel/workqueue.c
===================================================================
--- usb-4.4.orig/kernel/workqueue.c
+++ usb-4.4/kernel/workqueue.c
@@ -1175,12 +1175,14 @@ out_put:
  * This function is safe to call from any context including IRQ handler.
  */
 static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
-			       unsigned long *flags)
+			       unsigned long *pflags)
 {
 	struct worker_pool *pool;
 	struct pool_workqueue *pwq;
+	unsigned long flags;
 
-	local_irq_save(*flags);
+	local_irq_save(flags);
+	*pflags = flags;
 
 	/* try to steal the timer if it exists */
 	if (is_dwork) {
@@ -1241,7 +1243,7 @@ static int try_to_grab_pending(struct wo
 	}
 	spin_unlock(&pool->lock);
 fail:
-	local_irq_restore(*flags);
+	local_irq_restore(flags);
 	if (work_is_canceling(work))
 		return -ENOENT;
 	cpu_relax();

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#1347806

FromSedat Dilek <sedat.dilek@gmail.com>
Date2016-03-02 07:40 +0100
Message-ID<r88BY-3Mu-5@gated-at.bofh.it>
In reply to#1346722
On 3/1/16, Alan Stern <stern@rowland.harvard.edu> wrote:
> On Tue, 1 Mar 2016, Sedat Dilek wrote:
>
>> On Tue, Oct 13, 2015 at 2:57 AM, Steven Rostedt <rostedt@goodmis.org>
>> wrote:
>> > On Sat, 3 Oct 2015 12:05:42 +0200
>> > Sedat Dilek <sedat.dilek@gmail.com> wrote:
>> >
>> >> So, at the beginning... dunno WTF is causing the problems - no
>> >> workaround for CLANG.
>> >
>> > Probably need to compile with gcc and with clang and look at the binary
>> > differences. Or at least what objdump shows.
>> >
>>
>> [ Hope to address this issue to the correct people - CCed some people
>> I taped on their nerves ]
>>
>> Not sure if I should open a new thread?
>> Please, some clear statements on this.
>> Thanks.
>>
>> The issue is still visible and alive.
>
> ...
>
>> [ FACT #3: TEST-CASE #2 ]
>>
>> The most reliable test-case is to simply unplug my external Logitech
>> USB mouse - saw this by accident.
>> YES, it was so simple.
>>
>> --- dmesg_4.5.0-rc6-2-llvmlinux-amd64.txt       2016-02-29
>> 21:23:56.399691975 +0100
>> +++ dmesg_4.5.0-rc6-2-llvmlinux-amd64_usbmouse-unplugged.txt
>> 2016-02-29 21:28:14.401832240 +0100
>> @@ -832,3 +832,75 @@
>>  [   66.529779] PPP BSD Compression module registered
>>  [   66.563013] PPP Deflate Compression module registered
>>  [   66.978977] usb 2-1.5: USB disconnect, device number 4
>> +[  321.937369] usb 2-1.4: USB disconnect, device number 3
>> +[  321.950810] BUG: sleeping function called from invalid context at
>> kernel/workqueue.c:2785
>> +[  321.950816] in_atomic(): 0, irqs_disabled(): 1, pid: 44, name:
>> kworker/2:1
>
>> +[  321.950885] hardirqs last  enabled at (47769):
>> [<ffffffff819426a2>] _raw_spin_unlock_irq+0x32/0x60
>> +[  321.950889] hardirqs last disabled at (47770):
>> [<ffffffff81115bdc>] del_timer_sync+0x3c/0x110
>> +[  321.950894] softirqs last  enabled at (47112):
>> [<ffffffff810871a2>] __do_softirq+0x5a2/0x610
>> +[  321.950898] softirqs last disabled at (47097):
>> [<ffffffff8108747c>] irq_exit+0x9c/0x120
>> +[  321.950903] CPU: 2 PID: 44 Comm: kworker/2:1 Not tainted
>> 4.5.0-rc6-2-llvmlinux-amd64 #1
>> +[  321.950905] Hardware name: SAMSUNG ELECTRONICS CO., LTD.
>> 530U3BI/530U4BI/530U4BH/530U3BI/530U4BI/530U4BH, BIOS 13XK 03/28/2013
>> +[  321.950908] Workqueue: usb_hub_wq hub_event
>> +[  321.950911]  ffff8800d3326948 0000000000000092 0000000000000000
>> ffff8800d4347568
>> +[  321.950915]  ffffffff814ba7d4 ffff8800d43474f8 ffff8800d4340cc0
>> ffff8800d4347568
>> +[  321.950919]  ffffffff810e28fd 0000000000000092 0000000000000096
>> ffff8800d43475a8
>> +[  321.950923] Call Trace:
>> +[  321.950927]  [<ffffffff814ba7d4>] dump_stack+0xa4/0xf0
>> +[  321.950931]  [<ffffffff810e28fd>] ? print_irqtrace_events+0xcd/0xe0
>> +[  321.950936]  [<ffffffff810bf495>] ___might_sleep+0x295/0x2b0
>> +[  321.950939]  [<ffffffff810bf18f>] __might_sleep+0x4f/0xc0
>> +[  321.950943]  [<ffffffff810a12ef>] start_flush_work+0x2f/0x2a0
>> +[  321.950946]  [<ffffffff810a129c>] flush_work+0x5c/0x80
>> +[  321.950949]  [<ffffffff810a125a>] ? flush_work+0x1a/0x80
>> +[  321.950953]  [<ffffffff810e247d>] ? trace_hardirqs_off+0xd/0x10
>> +[  321.950956]  [<ffffffff810a032a>] ? try_to_grab_pending+0x4a/0x260
>> +[  321.950960]  [<ffffffff810a1717>] __cancel_work_timer+0x197/0x290
>> +[  321.950963]  [<ffffffff81115b8d>] ? try_to_del_timer_sync+0xad/0xc0
>> +[  321.950966]  [<ffffffff810a1578>] cancel_work_sync+0x18/0x20
>
> It's possible that this could be a compiler-related error connected
> with local_irq_save().  __cancel_work_timer() calls
>
> 		ret = try_to_grab_pending(work, is_dwork, &flags);
>
> and try_to_grab_pending() starts this way:
>
> static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
> 			       unsigned long *flags)
> {
> 	struct worker_pool *pool;
> 	struct pool_workqueue *pwq;
>
> 	local_irq_save(*flags);
>
> Then later on, __cancel_work_timer() does
>
> 	local_irq_restore(flags);
>
> Maybe CLANG doesn't like local_irq_save() applied to a pointer as
> opposed to a stack variable.
>
> As a quick test, try applying the patch below.  (Note that there is a
> similar construction in kernel/signal.c.)
>
> Alan Stern
>
>
>
> Index: usb-4.4/kernel/workqueue.c
> ===================================================================
> --- usb-4.4.orig/kernel/workqueue.c
> +++ usb-4.4/kernel/workqueue.c
> @@ -1175,12 +1175,14 @@ out_put:
>   * This function is safe to call from any context including IRQ handler.
>   */
>  static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
> -			       unsigned long *flags)
> +			       unsigned long *pflags)
>  {
>  	struct worker_pool *pool;
>  	struct pool_workqueue *pwq;
> +	unsigned long flags;
>
> -	local_irq_save(*flags);
> +	local_irq_save(flags);
> +	*pflags = flags;
>
>  	/* try to steal the timer if it exists */
>  	if (is_dwork) {
> @@ -1241,7 +1243,7 @@ static int try_to_grab_pending(struct wo
>  	}
>  	spin_unlock(&pool->lock);
>  fail:
> -	local_irq_restore(*flags);
> +	local_irq_restore(flags);
>  	if (work_is_canceling(work))
>  		return -ENOENT;
>  	cpu_relax();
>
>

might_sleep() is invoked in start_flush_work(), but there are no
"flags" passed to local_irq_{disable,enable}.

What about something like this?

@@ -2781,13 +2783,14 @@ static bool start_flush_work(struct
work_struct *work, struct wq_barrier *barr)
        struct worker *worker = NULL;
        struct worker_pool *pool;
        struct pool_workqueue *pwq;
+       unsigned long flags;

        might_sleep();

-       local_irq_disable();
+       local_irq_disable(flags);
        pool = get_work_pool(work);
        if (!pool) {
-               local_irq_enable();
+               local_irq_enable(flags);
                return false;
        }

- Sedat -

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#1347852

FromJiri Kosina <jikos@kernel.org>
Date2016-03-02 09:40 +0100
Message-ID<r8au6-56E-3@gated-at.bofh.it>
In reply to#1347806
On Wed, 2 Mar 2016, Sedat Dilek wrote:
> 
> static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr)
> {
>         struct worker *worker = NULL;
>         struct worker_pool *pool;
>         struct pool_workqueue *pwq;
> 
>         might_sleep();
> 
>         local_irq_disable();
>         pool = get_work_pool(work);
>         if (!pool) {
>                 local_irq_enable();
>                 return false;
>         }
> 
>         spin_lock(&pool->lock); <--- XXX: spin_lock_irq() ???

No, this is fine. IRQs are unconditionally disabled a few lines above.

-- 
Jiri Kosina
SUSE Labs

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#1347874

FromSedat Dilek <sedat.dilek@gmail.com>
Date2016-03-02 10:20 +0100
Message-ID<r8b6O-5Co-11@gated-at.bofh.it>
In reply to#1347852
On 3/2/16, Jiri Kosina <jikos@kernel.org> wrote:
> On Wed, 2 Mar 2016, Sedat Dilek wrote:
>>
>> static bool start_flush_work(struct work_struct *work, struct wq_barrier
>> *barr)
>> {
>>         struct worker *worker = NULL;
>>         struct worker_pool *pool;
>>         struct pool_workqueue *pwq;
>>
>>         might_sleep();
>>
>>         local_irq_disable();
>>         pool = get_work_pool(work);
>>         if (!pool) {
>>                 local_irq_enable();
>>                 return false;
>>         }
>>
>>         spin_lock(&pool->lock); <--- XXX: spin_lock_irq() ???
>
> No, this is fine. IRQs are unconditionally disabled a few lines above.
>

You are right, I tried with a substitution and that does not matter.

What about passing flags to local_irq_XXX?
And how do I do that?

- Sedat -

> --
> Jiri Kosina
> SUSE Labs
>
>

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#1347854

FromSedat Dilek <sedat.dilek@gmail.com>
Date2016-03-02 09:40 +0100
Message-ID<r8au6-56E-5@gated-at.bofh.it>
In reply to#1347806
On 3/2/16, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> On 3/1/16, Alan Stern <stern@rowland.harvard.edu> wrote:
>> On Tue, 1 Mar 2016, Sedat Dilek wrote:
>>
>>> On Tue, Oct 13, 2015 at 2:57 AM, Steven Rostedt <rostedt@goodmis.org>
>>> wrote:
>>> > On Sat, 3 Oct 2015 12:05:42 +0200
>>> > Sedat Dilek <sedat.dilek@gmail.com> wrote:
>>> >
>>> >> So, at the beginning... dunno WTF is causing the problems - no
>>> >> workaround for CLANG.
>>> >
>>> > Probably need to compile with gcc and with clang and look at the
>>> > binary
>>> > differences. Or at least what objdump shows.
>>> >
>>>
>>> [ Hope to address this issue to the correct people - CCed some people
>>> I taped on their nerves ]
>>>
>>> Not sure if I should open a new thread?
>>> Please, some clear statements on this.
>>> Thanks.
>>>
>>> The issue is still visible and alive.
>>
>> ...
>>
>>> [ FACT #3: TEST-CASE #2 ]
>>>
>>> The most reliable test-case is to simply unplug my external Logitech
>>> USB mouse - saw this by accident.
>>> YES, it was so simple.
>>>
>>> --- dmesg_4.5.0-rc6-2-llvmlinux-amd64.txt       2016-02-29
>>> 21:23:56.399691975 +0100
>>> +++ dmesg_4.5.0-rc6-2-llvmlinux-amd64_usbmouse-unplugged.txt
>>> 2016-02-29 21:28:14.401832240 +0100
>>> @@ -832,3 +832,75 @@
>>>  [   66.529779] PPP BSD Compression module registered
>>>  [   66.563013] PPP Deflate Compression module registered
>>>  [   66.978977] usb 2-1.5: USB disconnect, device number 4
>>> +[  321.937369] usb 2-1.4: USB disconnect, device number 3
>>> +[  321.950810] BUG: sleeping function called from invalid context at
>>> kernel/workqueue.c:2785
>>> +[  321.950816] in_atomic(): 0, irqs_disabled(): 1, pid: 44, name:
>>> kworker/2:1
>>
>>> +[  321.950885] hardirqs last  enabled at (47769):
>>> [<ffffffff819426a2>] _raw_spin_unlock_irq+0x32/0x60
>>> +[  321.950889] hardirqs last disabled at (47770):
>>> [<ffffffff81115bdc>] del_timer_sync+0x3c/0x110
>>> +[  321.950894] softirqs last  enabled at (47112):
>>> [<ffffffff810871a2>] __do_softirq+0x5a2/0x610
>>> +[  321.950898] softirqs last disabled at (47097):
>>> [<ffffffff8108747c>] irq_exit+0x9c/0x120
>>> +[  321.950903] CPU: 2 PID: 44 Comm: kworker/2:1 Not tainted
>>> 4.5.0-rc6-2-llvmlinux-amd64 #1
>>> +[  321.950905] Hardware name: SAMSUNG ELECTRONICS CO., LTD.
>>> 530U3BI/530U4BI/530U4BH/530U3BI/530U4BI/530U4BH, BIOS 13XK 03/28/2013
>>> +[  321.950908] Workqueue: usb_hub_wq hub_event
>>> +[  321.950911]  ffff8800d3326948 0000000000000092 0000000000000000
>>> ffff8800d4347568
>>> +[  321.950915]  ffffffff814ba7d4 ffff8800d43474f8 ffff8800d4340cc0
>>> ffff8800d4347568
>>> +[  321.950919]  ffffffff810e28fd 0000000000000092 0000000000000096
>>> ffff8800d43475a8
>>> +[  321.950923] Call Trace:
>>> +[  321.950927]  [<ffffffff814ba7d4>] dump_stack+0xa4/0xf0
>>> +[  321.950931]  [<ffffffff810e28fd>] ? print_irqtrace_events+0xcd/0xe0
>>> +[  321.950936]  [<ffffffff810bf495>] ___might_sleep+0x295/0x2b0
>>> +[  321.950939]  [<ffffffff810bf18f>] __might_sleep+0x4f/0xc0
>>> +[  321.950943]  [<ffffffff810a12ef>] start_flush_work+0x2f/0x2a0
>>> +[  321.950946]  [<ffffffff810a129c>] flush_work+0x5c/0x80
>>> +[  321.950949]  [<ffffffff810a125a>] ? flush_work+0x1a/0x80
>>> +[  321.950953]  [<ffffffff810e247d>] ? trace_hardirqs_off+0xd/0x10
>>> +[  321.950956]  [<ffffffff810a032a>] ? try_to_grab_pending+0x4a/0x260
>>> +[  321.950960]  [<ffffffff810a1717>] __cancel_work_timer+0x197/0x290
>>> +[  321.950963]  [<ffffffff81115b8d>] ? try_to_del_timer_sync+0xad/0xc0
>>> +[  321.950966]  [<ffffffff810a1578>] cancel_work_sync+0x18/0x20
>>
>> It's possible that this could be a compiler-related error connected
>> with local_irq_save().  __cancel_work_timer() calls
>>
>> 		ret = try_to_grab_pending(work, is_dwork, &flags);
>>
>> and try_to_grab_pending() starts this way:
>>
>> static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
>> 			       unsigned long *flags)
>> {
>> 	struct worker_pool *pool;
>> 	struct pool_workqueue *pwq;
>>
>> 	local_irq_save(*flags);
>>
>> Then later on, __cancel_work_timer() does
>>
>> 	local_irq_restore(flags);
>>
>> Maybe CLANG doesn't like local_irq_save() applied to a pointer as
>> opposed to a stack variable.
>>
>> As a quick test, try applying the patch below.  (Note that there is a
>> similar construction in kernel/signal.c.)
>>
>> Alan Stern
>>
>>
>>
>> Index: usb-4.4/kernel/workqueue.c
>> ===================================================================
>> --- usb-4.4.orig/kernel/workqueue.c
>> +++ usb-4.4/kernel/workqueue.c
>> @@ -1175,12 +1175,14 @@ out_put:
>>   * This function is safe to call from any context including IRQ handler.
>>   */
>>  static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
>> -			       unsigned long *flags)
>> +			       unsigned long *pflags)
>>  {
>>  	struct worker_pool *pool;
>>  	struct pool_workqueue *pwq;
>> +	unsigned long flags;
>>
>> -	local_irq_save(*flags);
>> +	local_irq_save(flags);
>> +	*pflags = flags;
>>
>>  	/* try to steal the timer if it exists */
>>  	if (is_dwork) {
>> @@ -1241,7 +1243,7 @@ static int try_to_grab_pending(struct wo
>>  	}
>>  	spin_unlock(&pool->lock);
>>  fail:
>> -	local_irq_restore(*flags);
>> +	local_irq_restore(flags);
>>  	if (work_is_canceling(work))
>>  		return -ENOENT;
>>  	cpu_relax();
>>
>>
>
> might_sleep() is invoked in start_flush_work(), but there are no
> "flags" passed to local_irq_{disable,enable}.
>
> What about something like this?
>
> @@ -2781,13 +2783,14 @@ static bool start_flush_work(struct
> work_struct *work, struct wq_barrier *barr)
>         struct worker *worker = NULL;
>         struct worker_pool *pool;
>         struct pool_workqueue *pwq;
> +       unsigned long flags;
>
>         might_sleep();
>
> -       local_irq_disable();
> +       local_irq_disable(flags);
>         pool = get_work_pool(work);
>         if (!pool) {
> -               local_irq_enable();
> +               local_irq_enable(flags);
>                 return false;
>         }
>

start_flush_work() is the only place where no flags are passed.
That stuff above does not work - no clue how to do that.
Any help?

Then I see there...
...
spin_lock(&pool->lock);
...
spin_unlock_irq(&pool->lock);
...

Should that be spin_lock_irq()?

static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr)
{
        struct worker *worker = NULL;
        struct worker_pool *pool;
        struct pool_workqueue *pwq;

        might_sleep();

        local_irq_disable();
        pool = get_work_pool(work);
        if (!pool) {
                local_irq_enable();
                return false;
        }

        spin_lock(&pool->lock); <--- XXX: spin_lock_irq() ???
        /* see the comment in try_to_grab_pending() with the same code */
        pwq = get_work_pwq(work);
        if (pwq) {
                if (unlikely(pwq->pool != pool))
                        goto already_gone;
        } else {
                worker = find_worker_executing_work(pool, work);
                if (!worker)
                        goto already_gone;
                pwq = worker->current_pwq;
        }

        check_flush_dependency(pwq->wq, work);

        insert_wq_barrier(pwq, barr, work, worker);
        spin_unlock_irq(&pool->lock);

        /*
         * If @max_active is 1 or rescuer is in use, flushing another work
         * item on the same workqueue may lead to deadlock.  Make sure the
         * flusher is not running on the same workqueue by verifying write
         * access.
         */
        if (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer)
                lock_map_acquire(&pwq->wq->lockdep_map);
        else
                lock_map_acquire_read(&pwq->wq->lockdep_map);
        lock_map_release(&pwq->wq->lockdep_map);

        return true;
already_gone:
        spin_unlock_irq(&pool->lock);
        return false;
}

- Sedat -

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