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workqueue: Mark up unlocked access to wq->first_flusher

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[ 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>
This commit is contained in:
Chris Wilson 2020-03-10 16:23:19 +00:00 committed by Tejun Heo
parent 2333e82995
commit 00d5d15b06
1 changed files with 2 additions and 2 deletions
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4
kernel/workqueue.c
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@ -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);