| From 959d1af8cffc8fd38ed53e8be1cf4ab8782f9c00 Mon Sep 17 00:00:00 2001 |
| From: Tejun Heo <tj@kernel.org> |
| Date: Fri, 3 Aug 2012 10:30:45 -0700 |
| Subject: workqueue: add missing smp_wmb() in process_one_work() |
| |
| From: Tejun Heo <tj@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 <tj@kernel.org> |
| Cc: Oleg Nesterov <oleg@redhat.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| kernel/workqueue.c | 2 ++ |
| 1 file changed, 2 insertions(+) |
| |
| --- 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); |