workqueue: Mark up unlocked access to wq->first_flusher
[ 7329.671518] BUG: KCSAN: data-race in flush_workqueue / flush_workqueue
[ 7329.671549]
[ 7329.671572] write to 0xffff8881f65fb250 of 8 bytes by task 37173 on cpu 2:
[ 7329.671607] flush_workqueue+0x3bc/0x9b0 (kernel/workqueue.c:2844)
[ 7329.672527]
[ 7329.672540] read to 0xffff8881f65fb250 of 8 bytes by task 37175 on cpu 0:
[ 7329.672571] flush_workqueue+0x28d/0x9b0 (kernel/workqueue.c:2835)
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 5afa9ad..40a4ba3 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2832,7 +2832,7 @@ void flush_workqueue(struct workqueue_struct *wq)
* First flushers are responsible for cascading flushes and
* handling overflow. Non-first flushers can simply return.
*/
- if (wq->first_flusher != &this_flusher)
+ if (READ_ONCE(wq->first_flusher) != &this_flusher)
return;
mutex_lock(&wq->mutex);
@@ -2841,7 +2841,7 @@ void flush_workqueue(struct workqueue_struct *wq)
if (wq->first_flusher != &this_flusher)
goto out_unlock;
- wq->first_flusher = NULL;
+ WRITE_ONCE(wq->first_flusher, NULL);
WARN_ON_ONCE(!list_empty(&this_flusher.list));
WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
