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workqueue: add missing smp_wmb() in process_one_work()

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WORK_STRUCT_PENDING is used to claim ownership of a work item and
process_one_work() releases it before starting execution.  When
someone else grabs PENDING, all pre-release updates to the work item
should be visible and all updates made by the new owner should happen
afterwards.

Grabbing PENDING uses test_and_set_bit() and thus has a full barrier;
however, clearing doesn't have a matching wmb.  Given the preceding
spin_unlock and use of clear_bit, I don't believe this can be a
problem on an actual machine and there hasn't been any related report
but it still is theretically possible for clear_pending to permeate
upwards and happen before work->entry update.

Add an explicit smp_wmb() before work_clear_pending().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: stable@vger.kernel.org
This commit is contained in:
Tejun Heo 2012-08-03 10:30:45 -07:00
parent d4283e9378
commit 959d1af8cf
1 changed files with 2 additions and 0 deletions
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2
kernel/workqueue.c
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@ -1997,7 +1997,9 @@ __acquires(&gcwq->lock)
spin_unlock_irq(&gcwq->lock);
smp_wmb(); /* paired with test_and_set_bit(PENDING) */
work_clear_pending(work);
lock_map_acquire_read(&cwq->wq->lockdep_map);
lock_map_acquire(&lockdep_map);
trace_workqueue_execute_start(work);