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authorLai Jiangshan <laijs@cn.fujitsu.com>2012-09-02 00:28:19 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-10-02 10:30:33 -0700
commit6adebb0e1d4820435e0c6739b0de20a196cc20d5 (patch)
tree2e572784e0ddf58832e1cc9aba859e365834f5a5 /kernel
parent956b165f9e89e37aff44d615321d1e3166589701 (diff)
workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic
commit 96e65306b81351b656835c15931d1d237b252f27 upstream. The compiler may compile the following code into TWO write/modify instructions. worker->flags &= ~WORKER_UNBOUND; worker->flags |= WORKER_REBIND; so the other CPU may temporarily see worker->flags which doesn't have either WORKER_UNBOUND or WORKER_REBIND set and perform local wakeup prematurely. Fix it by using single explicit assignment via ACCESS_ONCE(). Because idle workers have another WORKER_NOT_RUNNING flag, this bug doesn't exist for them; however, update it to use the same pattern for consistency. tj: Applied the change to idle workers too and updated comments and patch description a bit. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/workqueue.c9
1 files changed, 6 insertions, 3 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f483dd0bc9c9..7584322349c1 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3433,14 +3433,17 @@ static int __cpuinit trustee_thread(void *__gcwq)
for_each_busy_worker(worker, i, pos, gcwq) {
struct work_struct *rebind_work = &worker->rebind_work;
+ unsigned long worker_flags = worker->flags;
/*
* Rebind_work may race with future cpu hotplug
* operations. Use a separate flag to mark that
- * rebinding is scheduled.
+ * rebinding is scheduled. The morphing should
+ * be atomic.
*/
- worker->flags |= WORKER_REBIND;
- worker->flags &= ~WORKER_ROGUE;
+ worker_flags |= WORKER_REBIND;
+ worker_flags &= ~WORKER_ROGUE;
+ ACCESS_ONCE(worker->flags) = worker_flags;
/* queue rebind_work, wq doesn't matter, use the default one */
if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,