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Date: Thu, 11 Oct 2012 07:53:14 +0900 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, alan@...rguk.ukuu.org.uk, Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com> Subject: [ 028/122] workqueue: add missing smp_wmb() in process_one_work() 3.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tejun Heo <tj@...nel.org> commit 959d1af8cffc8fd38ed53e8be1cf4ab8782f9c00 upstream. 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@...nel.org> Cc: Oleg Nesterov <oleg@...hat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- kernel/workqueue.c | 2 ++ 1 file changed, 2 insertions(+) --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -2073,7 +2073,9 @@ __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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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