workqueue: fix race condition in unbound workqueue free path (bc0caf09) · Commits · 戴 / test

("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>

kernel/workqueue.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -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);
		}

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