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Groups > linux.kernel > #1269608
| From | Ben Hutchings <ben@decadent.org.uk> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH 3.2 26/60] sched/core: Fix TASK_DEAD race in finish_task_switch() |
| Date | 2015-11-15 03:20 +0100 |
| Message-ID | <quV59-3JS-41@gated-at.bofh.it> (permalink) |
| References | <quUVr-3GF-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
3.2.73-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Peter Zijlstra <peterz@infradead.org>
commit 95913d97914f44db2b81271c2e2ebd4d2ac2df83 upstream.
So the problem this patch is trying to address is as follows:
CPU0 CPU1
context_switch(A, B)
ttwu(A)
LOCK A->pi_lock
A->on_cpu == 0
finish_task_switch(A)
prev_state = A->state <-.
WMB |
A->on_cpu = 0; |
UNLOCK rq0->lock |
| context_switch(C, A)
`-- A->state = TASK_DEAD
prev_state == TASK_DEAD
put_task_struct(A)
context_switch(A, C)
finish_task_switch(A)
A->state == TASK_DEAD
put_task_struct(A)
The argument being that the WMB will allow the load of A->state on CPU0
to cross over and observe CPU1's store of A->state, which will then
result in a double-drop and use-after-free.
Now the comment states (and this was true once upon a long time ago)
that we need to observe A->state while holding rq->lock because that
will order us against the wakeup; however the wakeup will not in fact
acquire (that) rq->lock; it takes A->pi_lock these days.
We can obviously fix this by upgrading the WMB to an MB, but that is
expensive, so we'd rather avoid that.
The alternative this patch takes is: smp_store_release(&A->on_cpu, 0),
which avoids the MB on some archs, but not important ones like ARM.
Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Cc: manfred@colorfullife.com
Cc: will.deacon@arm.com
Fixes: e4a52bcb9a18 ("sched: Remove rq->lock from the first half of ttwu()")
Link: http://lkml.kernel.org/r/20150929124509.GG3816@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.2:
- Adjust filename
- As smp_store_release() is not defined, use smp_mb()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1016,8 +1016,10 @@ static inline void finish_lock_switch(st
* After ->on_cpu is cleared, the task can be moved to a different CPU.
* We must ensure this doesn't happen until the switch is completely
* finished.
+ *
+ * Pairs with the control dependency and rmb in try_to_wake_up().
*/
- smp_wmb();
+ smp_mb();
prev->on_cpu = 0;
#endif
#ifdef CONFIG_DEBUG_SPINLOCK
@@ -3191,11 +3192,11 @@ static void finish_task_switch(struct rq
* If a task dies, then it sets TASK_DEAD in tsk->state and calls
* schedule one last time. The schedule call will never return, and
* the scheduled task must drop that reference.
- * The test for TASK_DEAD must occur while the runqueue locks are
- * still held, otherwise prev could be scheduled on another cpu, die
- * there before we look at prev->state, and then the reference would
- * be dropped twice.
- * Manfred Spraul <manfred@colorfullife.com>
+ *
+ * We must observe prev->state before clearing prev->on_cpu (in
+ * finish_lock_switch), otherwise a concurrent wakeup can get prev
+ * running on another CPU and we could rave with its RUNNING -> DEAD
+ * transition, resulting in a double drop.
*/
prev_state = prev->state;
finish_arch_switch(prev);
--
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[PATCH 3.2 00/60] 3.2.73-rc1 review Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:10 +0100
[PATCH 3.2 43/60] dm btree remove: fix a bug when rebalancing nodes after removal Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:10 +0100
[PATCH 3.2 27/60] 3w-9xxx: don't unmap bounce buffered commands Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:10 +0100
[PATCH 3.2 12/60] genirq: Fix race in register_irq_proc() Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:10 +0100
[PATCH 3.2 31/60] iommu/vt-d: fix range computation when making room for large pages Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:10 +0100
[PATCH 3.2 28/60] xen-blkfront: check for null drvdata in blkback_changed (XenbusStateClosing) Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:10 +0100
[PATCH 3.2 32/60] xhci: don't finish a TD if we get a short transfer event mid TD Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:10 +0100
[PATCH 3.2 46/60] md/raid1: don't clear bitmap bit when bad-block-list write fails. Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:10 +0100
[PATCH 3.2 24/60] iwlwifi: dvm: fix D3 firmware PN programming Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:10 +0100
[PATCH 3.2 04/60] regmap: debugfs: Don't bother actually printing when calculating max length Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:10 +0100
[PATCH 3.2 55/60] asix: Don't reset PHY on if_up for ASIX 88772 Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 08/60] UBI: Validate data_size Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 53/60] skbuff: Fix skb checksum partial check. Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 38/60] IB/cm: Fix rb-tree duplicate free and use-after-free Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 20/60] usb: Add device quirk for Logitech PTZ cameras Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 33/60] xhci: handle no ping response error properly Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 19/60] USB: Add reset-resume quirk for two Plantronics usb headphones. Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 44/60] dm btree: fix leak of bufio-backed block in btree_split_beneath error path Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 40/60] powerpc/rtas: Validate rtas.entry before calling enter_rtas() Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 34/60] xhci: Switch Intel Lynx Point LP ports to EHCI on shutdown. Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 07/60] x86/xen: Do not clip xen_e820_map to xen_e820_map_entries when sanitizing map Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 03/60] regmap: debugfs: Ensure we don't underflow when printing access masks Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 51/60] net: add length argument to skb_copy_and_csum_datagram_iovec Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 05/60] ath9k: declare required extra tx headroom Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 39/60] drm/nouveau/gem: return only valid domain when there's only one Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 06/60] m68k: Define asmlinkage_protect Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 26/60] sched/core: Fix TASK_DEAD race in finish_task_switch() Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 45/60] md/raid1: ensure device failure recorded before write request returns. Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 15/60] md/raid0: update queue parameter in a safer location. Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 59/60] KEYS: Fix race between key destruction and finding a keyring by name Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 23/60] ppp: don't override sk->sk_state in pppoe_flush_dev() Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 49/60] mvsas: Fix NULL pointer dereference in mvs_slot_task_free Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 58/60] KVM: x86: work around infinite loop in microcode when #AC is delivered Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:20 +0100
[PATCH 3.2 42/60] ppp: fix pppoe_dev deletion condition in pppoe_release() Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:30 +0100
[PATCH 3.2 10/60] MIPS: dma-default: Fix 32-bit fall back to GFP_DMA Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:30 +0100
[PATCH 3.2 50/60] sched: declare pid_alive as inline Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:30 +0100
[PATCH 3.2 17/60] clocksource: Fix abs() usage w/ 64bit values Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:30 +0100
[PATCH 3.2 36/60] crypto: api - Only abort operations on fatal signal Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:30 +0100
[PATCH 3.2 16/60] md/raid0: apply base queue limits *before* disk_stack_limits Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:30 +0100
[PATCH 3.2 47/60] md/raid10: ensure device failure recorded before write request returns. Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:30 +0100
[PATCH 3.2 57/60] Failing to send a CLOSE if file is opened WRONLY and server reboots on a 4.x mount Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:30 +0100
[PATCH 3.2 14/60] [SMB3] Do not fall back to SMBWriteX in set_file_size error cases Ben Hutchings <ben@decadent.org.uk> - 2015-11-15 03:30 +0100
Re: [PATCH 3.2 00/60] 3.2.73-rc1 review Guenter Roeck <linux@roeck-us.net> - 2015-11-15 14:50 +0100
Re: [PATCH 3.2 00/60] 3.2.73-rc1 review Ben Hutchings <ben@decadent.org.uk> - 2015-11-16 12:20 +0100
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