blk-mq: fix queue reference leak on blk_mq_alloc_disk_for_queue failure

Drop the request queue reference just acquired when __alloc_disk_node
failed.

Fixes: 6f8191f ("block: simplify disk shutdown")
Reported-by: Al Viro <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Christoph Hellwig

block/blk-mq.c

@@ -4045,9 +4045,14 @@ EXPORT_SYMBOL(__blk_mq_alloc_disk);
 struct gendisk *blk_mq_alloc_disk_for_queue(struct request_queue *q,
 		struct lock_class_key *lkclass)
 {
+	struct gendisk *disk;
+
 	if (!blk_get_queue(q))
 		return NULL;
-	return __alloc_disk_node(q, NUMA_NO_NODE, lkclass);
+	disk = __alloc_disk_node(q, NUMA_NO_NODE, lkclass);
+	if (!disk)
+		blk_put_queue(q);
+	return disk;
 }
 EXPORT_SYMBOL(blk_mq_alloc_disk_for_queue);