Commit 0e626368 authored Sep 27, 2015 by Akinobu Mita Committed by Jens Axboe Sep 29, 2015

blk-mq: fix q->mq_usage_counter access race



CPU hotplug handling for blk-mq (blk_mq_queue_reinit) accesses
q->mq_usage_counter while freezing all request queues in all_q_list.
On the other hand, q->mq_usage_counter is deinitialized in
blk_mq_free_queue() before deleting the queue from all_q_list.

So if CPU hotplug event occurs in the window, percpu_ref_kill() is
called with q->mq_usage_counter which has already been marked dead,
and it triggers warning.  Fix it by deleting the queue from all_q_list
earlier than destroying q->mq_usage_counter.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent a723bab3

block/blk-mq.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -2067,15 +2067,16 @@ void blk_mq_free_queue(struct request_queue *q)
		{
		struct blk_mq_tag_set *set = q->tag_set;

		mutex_lock(&all_q_mutex);
		list_del_init(&q->all_q_node);
		mutex_unlock(&all_q_mutex);

		blk_mq_del_queue_tag_set(q);

		blk_mq_exit_hw_queues(q, set, set->nr_hw_queues);
		blk_mq_free_hw_queues(q, set);

		percpu_ref_exit(&q->mq_usage_counter);
		mutex_lock(&all_q_mutex);
		list_del_init(&q->all_q_node);
		mutex_unlock(&all_q_mutex);
		}

		/* Basically redo blk_mq_init_queue with queue frozen */

Admin message