block: move queue freezing & elevator_lock into elevator_change()

Move queue freezing & elevator_lock into elevator_change(), and prepare
for using elevator_change() for setting up & tearing down default elevator
too.

Also add lockdep_assert_held() in __elevator_change() because either
read or write lock is required for changing elevator.

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>
Link: https://lore.kernel.org/r/20250505141805.2751237-15-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/elevator.c b/block/elevator.c
index cabd7a8bb76c1d015763baf61aa38eef5a181ea8..cb54a3791fe5d0ed22867b35fd0480ff39e17733 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -676,10 +676,19 @@ out_unfreeze:
  */
 static int elevator_change(struct request_queue *q, const char *elevator_name)
 {
-       if (q->elevator && elevator_match(q->elevator->type, elevator_name))
-               return 0;
+       unsigned int memflags;
+       int ret = 0;
 
-       return elevator_switch(q, elevator_name);
+       lockdep_assert_held(&q->tag_set->update_nr_hwq_lock);
+
+       memflags = blk_mq_freeze_queue(q);
+       mutex_lock(&q->elevator_lock);
+       if (!(q->elevator && elevator_match(q->elevator->type,
+                               elevator_name)))
+               ret = elevator_switch(q, elevator_name);
+       mutex_unlock(&q->elevator_lock);
+       blk_mq_unfreeze_queue(q, memflags);
+       return ret;
 }
 
 /*
@@ -718,7 +727,6 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
        char elevator_name[ELV_NAME_MAX];
        char *name;
        int ret;
-       unsigned int memflags;
        struct request_queue *q = disk->queue;
        struct blk_mq_tag_set *set = q->tag_set;
 
@@ -737,13 +745,9 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
        elv_iosched_load_module(name);
 
        down_read(&set->update_nr_hwq_lock);
-       memflags = blk_mq_freeze_queue(q);
-       mutex_lock(&q->elevator_lock);
        ret = elevator_change(q, name);
        if (!ret)
                ret = count;
-       mutex_unlock(&q->elevator_lock);
-       blk_mq_unfreeze_queue(q, memflags);
        up_read(&set->update_nr_hwq_lock);
        return ret;
 }