[PATCH 2/2] block: avoid unnecessary queue freeze in elevator_set_none()

[Ming Lei <ming.lei@redhat.com>]

elevator_set_none() is called when deleting disk, in which queue has been
un-registered, and elevator switch can't happen any more.

So if q->elevator is NULL, it is not necessary to freeze queue and drain
IO any more.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/elevator.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/block/elevator.c b/block/elevator.c
index e1386b84a415..35f4de749dcd 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -754,8 +754,18 @@ void elevator_set_none(struct request_queue *q)
 		.name	= "none",
 		.quiesce_queue = true,
 	};
+	bool need_change;
 	int err;
 
+	WARN_ON_ONCE(blk_queue_registered(q));
+
+	/* queue has been unregisted, elevator can't be switched anymore */
+	mutex_lock(&q->elevator_lock);
+	need_change = !!q->elevator;
+	mutex_unlock(&q->elevator_lock);
+	if (!need_change)
+		return;
+
 	err = elevator_change(q, &ctx);
 	if (err < 0)
 		pr_warn("%s: set none elevator failed %d\n", __func__, err);
-- 
2.47.0