Commit cddd5d17 authored Aug 16, 2014 by Tejun Heo Committed by Jens Axboe Aug 21, 2014

blk-mq: blk_mq_freeze_queue() should allow nesting



While converting to percpu_ref for freezing, add703fd ("blk-mq:
use percpu_ref for mq usage count") incorrectly made
blk_mq_freeze_queue() misbehave when freezing is nested due to
percpu_ref_kill() being invoked on an already killed ref.

Fix it by making blk_mq_freeze_queue() kill and kick the queue only
for the outermost freeze attempt.  All the nested ones can simply wait
for the ref to reach zero.

While at it, remove unnecessary @wake initialization from
blk_mq_unfreeze_queue().

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent a68aafa5

block/blk-mq.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -112,18 +112,22 @@ static void blk_mq_usage_counter_release(struct percpu_ref *ref)
		*/
		void blk_mq_freeze_queue(struct request_queue *q)
		{
		bool freeze;

		spin_lock_irq(q->queue_lock);
		q->mq_freeze_depth++;
		freeze = !q->mq_freeze_depth++;
		spin_unlock_irq(q->queue_lock);

		if (freeze) {
		percpu_ref_kill(&q->mq_usage_counter);
		blk_mq_run_queues(q, false);
		}
		wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter));
		}

		static void blk_mq_unfreeze_queue(struct request_queue *q)
		{
		bool wake = false;
		bool wake;

		spin_lock_irq(q->queue_lock);
		wake = !--q->mq_freeze_depth;

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