workqueue: Fix pwq ref leak in rescuer_thread() (e66b39af) · Commits · 戴 / test

("workqueue: allow rescuer thread to do more work.") made the rescuer worker requeue the pwq immediately if there may be more work items which need rescuing instead of waiting for the next mayday timer expiration. Unfortunately, it doesn't check whether the pwq is already on the mayday list and unconditionally gets the ref and moves it onto the list. This doesn't corrupt the list but creates an additional reference to the pwq. It got queued twice but will only be removed once. This leak later can trigger pwq refcnt warning on workqueue destruction and prevent freeing of the workqueue. Signed-off-by:

Tejun Heo <tj@kernel.org> Cc: "Williams, Gerald S" <gerald.s.williams@intel.com> Cc: NeilBrown <neilb@suse.de> Cc: stable@vger.kernel.org # v3.19+

kernel/workqueue.c

+12 −5

Original line number	Diff line number	Diff line
		@@ -2533,8 +2533,14 @@ repeat:
		*/
		if (need_to_create_worker(pool)) {
		spin_lock(&wq_mayday_lock);
		/*
		* Queue iff we aren't racing destruction
		* and somebody else hasn't queued it already.
		*/
		if (wq->rescuer && list_empty(&pwq->mayday_node)) {
		get_pwq(pwq);
		list_move_tail(&pwq->mayday_node, &wq->maydays);
		list_add_tail(&pwq->mayday_node, &wq->maydays);
		}
		spin_unlock(&wq_mayday_lock);
		}
		}
		@@ -4374,8 +4380,8 @@ void destroy_workqueue(struct workqueue_struct *wq)
		for_each_pwq(pwq, wq) {
		spin_lock_irq(&pwq->pool->lock);
		if (WARN_ON(pwq_busy(pwq))) {
		pr_warning("%s: %s has the following busy pwq (refcnt=%d)\n",
		__func__, wq->name, pwq->refcnt);
		pr_warning("%s: %s has the following busy pwq\n",
		__func__, wq->name);
		show_pwq(pwq);
		spin_unlock_irq(&pwq->pool->lock);
		mutex_unlock(&wq->mutex);
		@@ -4670,7 +4676,8 @@ static void show_pwq(struct pool_workqueue *pwq)
		pr_info(" pwq %d:", pool->id);
		pr_cont_pool_info(pool);

		pr_cont(" active=%d/%d%s\n", pwq->nr_active, pwq->max_active,
		pr_cont(" active=%d/%d refcnt=%d%s\n",
		pwq->nr_active, pwq->max_active, pwq->refcnt,
		!list_empty(&pwq->mayday_node) ? " MAYDAY" : "");

		hash_for_each(pool->busy_hash, bkt, worker, hentry) {

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