3.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Tejun Heo <t...@kernel.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 <t...@kernel.org>
Cc: Oleg Nesterov <o...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
kernel/workqueue.c | 2 ++
1 file changed, 2 insertions(+)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1864,7 +1864,9 @@ __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);
--
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