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authorLai Jiangshan <laijs@cn.fujitsu.com>2012-09-02 00:28:19 +0800
committerTejun Heo <tj@kernel.org>2012-09-04 17:04:45 -0700
commit96e65306b81351b656835c15931d1d237b252f27 (patch)
treeaf06187bebae44b48ca8e68a639a4ddc6b0a3509 /kernel/workqueue.c
parent0d7614f09c1ebdbaa1599a5aba7593f147bf96ee (diff)
workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic
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> Cc: stable@vger.kernel.org
Diffstat (limited to 'kernel/workqueue.c')
-rw-r--r--kernel/workqueue.c17
1 files changed, 11 insertions, 6 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 692d97628a1..c462cd60c37 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1396,12 +1396,15 @@ retry:
/* set REBIND and kick idle ones, we'll wait for these later */
for_each_worker_pool(pool, gcwq) {
list_for_each_entry(worker, &pool->idle_list, entry) {
+ unsigned long worker_flags = worker->flags;
+
if (worker->flags & WORKER_REBIND)
continue;
- /* morph UNBOUND to REBIND */
- worker->flags &= ~WORKER_UNBOUND;
- worker->flags |= WORKER_REBIND;
+ /* morph UNBOUND to REBIND atomically */
+ worker_flags &= ~WORKER_UNBOUND;
+ worker_flags |= WORKER_REBIND;
+ ACCESS_ONCE(worker->flags) = worker_flags;
idle_rebind.cnt++;
worker->idle_rebind = &idle_rebind;
@@ -1434,10 +1437,12 @@ retry:
/* rebind busy workers */
for_each_busy_worker(worker, i, pos, gcwq) {
struct work_struct *rebind_work = &worker->rebind_work;
+ unsigned long worker_flags = worker->flags;
- /* morph UNBOUND to REBIND */
- worker->flags &= ~WORKER_UNBOUND;
- worker->flags |= WORKER_REBIND;
+ /* morph UNBOUND to REBIND atomically */
+ worker_flags &= ~WORKER_UNBOUND;
+ worker_flags |= WORKER_REBIND;
+ ACCESS_ONCE(worker->flags) = worker_flags;
if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
work_data_bits(rebind_work)))