blk-mq: blk_mq_freeze_queue() should allow nesting

While converting to percpu_ref for freezing, add703fda981 ("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>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index a0565bb20fd556c42e610732c07c49d2a3f84ce8..7950f8d7c1bb182b25aa9df8d41910941fc0022d 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -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;