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blk-mq: blk_mq_freeze_queue() should allow nesting 

While converting to percpu_ref for freezing, add703fda9 ("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>
This commit is contained in:
Tejun Heo 2014-08-16 08:02:24 -04:00 committed by Jens Axboe
parent a68aafa5b2
commit cddd5d1764
1 changed files with 8 additions and 4 deletions
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12
block/blk-mq.c
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@ -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);
percpu_ref_kill(&q->mq_usage_counter);
blk_mq_run_queues(q, false);
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;