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Commit 0e626368 authored by Akinobu Mita's avatar Akinobu Mita Committed by Jens Axboe
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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: default avatarAkinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: default avatarMing Lei <tom.leiming@gmail.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens 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 */