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authorTejun Heo <tj@kernel.org>2012-08-03 10:30:45 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-10-13 05:28:03 +0900
commit21de4eb26ec0b1b9c484da823fbcd1d3a48afec9 (patch)
treeec3e1821f50f68c7d18a9626c8a5455e943a782a /kernel
parentfe77d1bb93b50233d9d2932d348c1a78214ea485 (diff)
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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 <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/workqueue.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 00c0bad..aef9452 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1868,7 +1868,9 @@ __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);