block: don't call freeze queue in elevator_switch() and elevator_disable()

JIRA: https://issues.redhat.com/browse/RHEL-106845

commit f8e111c
Author: Ming Lei <ming.lei@redhat.com>
Date:   Mon May 5 22:17:41 2025 +0800

    block: don't call freeze queue in elevator_switch() and elevator_disable()

    Both elevator_switch() and elevator_disable() are only called from the
    two code paths, in which queue is guaranteed to be frozen.

    So don't call freeze queue in the two functions, also add asserts for
    queue freeze.

    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: Hannes Reinecke <hare@suse.de>
    Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
    Signed-off-by: Ming Lei <ming.lei@redhat.com>
    Reviewed-by: Yu Kuai <yukuai3@huawei.com>
    Link: https://lore.kernel.org/r/20250505141805.2751237-4-ming.lei@redhat.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

block/elevator.c

@@ -615,12 +615,11 @@ void elevator_init_mq(struct request_queue *q)
  */
 int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 {
-	unsigned int memflags;
 	int ret;
 
+	WARN_ON_ONCE(q->mq_freeze_depth == 0);
 	lockdep_assert_held(&q->elevator_lock);
 
-	memflags = blk_mq_freeze_queue(q);
 	blk_mq_quiesce_queue(q);
 
 	if (q->elevator) {
@@ -641,7 +640,6 @@ int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 
 out_unfreeze:
 	blk_mq_unquiesce_queue(q);
-	blk_mq_unfreeze_queue(q, memflags);
 
 	if (ret) {
 		pr_warn("elv: switch to \"%s\" failed, falling back to \"none\"\n",
@@ -653,11 +651,9 @@ int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 
 void elevator_disable(struct request_queue *q)
 {
-	unsigned int memflags;
-
+	WARN_ON_ONCE(q->mq_freeze_depth == 0);
 	lockdep_assert_held(&q->elevator_lock);
 
-	memflags = blk_mq_freeze_queue(q);
 	blk_mq_quiesce_queue(q);
 
 	elv_unregister_queue(q);
@@ -668,7 +664,6 @@ void elevator_disable(struct request_queue *q)
 	blk_add_trace_msg(q, "elv switch: none");
 
 	blk_mq_unquiesce_queue(q);
-	blk_mq_unfreeze_queue(q, memflags);
 }
 
 /*