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workqueue: fix race condition in unbound workqueue free path

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8864b4e59 ("workqueue: implement get/put_pwq()") implemented pwq
(pool_workqueue) refcnting which frees workqueue when the last pwq
goes away.  It determined whether it was the last pwq by testing
wq->pwqs is empty.  Unfortunately, the test was done outside wq->mutex
and multiple pwq release could race and try to free wq multiple times
leading to oops.

Test wq->pwqs emptiness while holding wq->mutex.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2013-04-01 11:23:31 -07:00
parent b592760547
commit bc0caf099d
1 changed files with 3 additions and 1 deletions
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4
kernel/workqueue.c
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@ -3534,6 +3534,7 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
unbound_release_work);
struct workqueue_struct *wq = pwq->wq;
struct worker_pool *pool = pwq->pool;
bool is_last;
if (WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND)))
return;
@ -3545,6 +3546,7 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
*/
mutex_lock(&wq->mutex);
list_del_rcu(&pwq->pwqs_node);
is_last = list_empty(&wq->pwqs);
mutex_unlock(&wq->mutex);
put_unbound_pool(pool);
@ -3554,7 +3556,7 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
* If we're the last pwq going away, @wq is already dead and no one
* is gonna access it anymore. Free it.
*/
if (list_empty(&wq->pwqs))
if (is_last)
kfree(wq);
}