[PATCH] blk-mq: Make blk_mq_quiesce_tagset() hold the tag list mutex less long

[Bart Van Assche <bvanassche@xxxxxxx>]

Make sure that the tag_list_lock mutex is no longer held than necessary.
This change reduces latency if e.g. blk_mq_quiesce_tagset() is called
concurrently from more than one thread. This function is used by the
NVMe core and also by the UFS driver.

Reported-by: Peter Wang <peter.wang@xxxxxxxxxxxx>
Cc: Chao Leng <lengchao@xxxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: commit 414dd48e882c ("blk-mq: add tagset quiesce interface")
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 block/blk-mq.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 4b2c8e940f59..1ef227dfb9ba 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -283,8 +283,9 @@ void blk_mq_quiesce_tagset(struct blk_mq_tag_set *set)
 		if (!blk_queue_skip_tagset_quiesce(q))
 			blk_mq_quiesce_queue_nowait(q);
 	}
-	blk_mq_wait_quiesce_done(set);
 	mutex_unlock(&set->tag_list_lock);
+
+	blk_mq_wait_quiesce_done(set);
 }
 EXPORT_SYMBOL_GPL(blk_mq_quiesce_tagset);