From: Tejun Heo Date: Fri, 3 Aug 2012 17:30:45 +0000 (-0700) Subject: workqueue: add missing smp_wmb() in process_one_work() X-Git-Tag: v3.5.7~112 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=aeda28cd8dcbf2bde2194a447225f83a4a430e8c;p=thirdparty%2Fkernel%2Fstable.git workqueue: add missing smp_wmb() in process_one_work() 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 Cc: Oleg Nesterov Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 2016347487265..478f2abbfbc3b 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1869,7 +1869,9 @@ __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);