block: use q->elevator with ->elevator_lock held in elv_iosched_show()

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

commit 94209d2
Author: Ming Lei <ming.lei@redhat.com>
Date:   Mon May 5 22:17:42 2025 +0800

    block: use q->elevator with ->elevator_lock held in elv_iosched_show()

    Use q->elevator with ->elevator_lock held in elv_iosched_show(), since
    the local cached elevator reference may become stale after getting
    ->elevator_lock.

    Reviewed-by: Hannes Reinecke <hare@suse.de>
    Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Ming Lei <ming.lei@redhat.com>
    Link: https://lore.kernel.org/r/20250505141805.2751237-5-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

@@ -739,7 +739,6 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
 ssize_t elv_iosched_show(struct gendisk *disk, char *name)
 {
 	struct request_queue *q = disk->queue;
-	struct elevator_queue *eq = q->elevator;
 	struct elevator_type *cur = NULL, *e;
 	int len = 0;
 
@@ -748,7 +747,7 @@ ssize_t elv_iosched_show(struct gendisk *disk, char *name)
 		len += sprintf(name+len, "[none] ");
 	} else {
 		len += sprintf(name+len, "none ");
-		cur = eq->type;
+		cur = q->elevator->type;
 	}
 
 	spin_lock(&elv_list_lock);