commit: 959d1af8cffc8fd38ed53e8be1cf4ab8782f9c00 From: Tejun Heo <[email protected]> Date: Fri, 3 Aug 2012 10:30:45 -0700 Subject: workqueue: add missing smp_wmb() in process_one_work()
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 <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: [email protected] --- kernel/workqueue.c | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 70f95ab..5c26d36 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -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); -- 1.7.3.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
