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

[ Upstream commit 94209d2 ]

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 <[email protected]>
Reviewed-by: Nilay Shroff <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: Ming Lei

block/elevator.c

@@ -744,7 +744,6 @@ 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;
 
@@ -753,7 +752,7 @@ 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);