block: release rq qos structures for queue without disk

blkcg_init_queue() may add rq qos structures to request queue, previously
blk_cleanup_queue() calls rq_qos_exit() to release them, but commit
8e141f9e ("block: drain file system I/O on del_gendisk")
moves rq_qos_exit() into del_gendisk(), so memory leak is caused
because queues may not have disk, such as un-present scsi luns, nvme
admin queue, ...

Fixes the issue by adding rq_qos_exit() to blk_cleanup_queue() back.

BTW, v5.18 won't need this patch any more since we move
blkcg_init_queue()/blkcg_exit_queue() into disk allocation/release
handler, and patches have been in for-5.18/block.

Cc: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Fixes: 8e141f9e ("block: drain file system I/O on del_gendisk")
Reported-by: syzbot+b42749a851a47a0f581b@syzkaller.appspotmail.com
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220314043018.177141-1-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -50,6 +50,7 @@
 #include "blk-mq-sched.h"
 #include "blk-pm.h"
 #include "blk-throttle.h"
+#include "blk-rq-qos.h"
 
 struct dentry *blk_debugfs_root;
 
@@ -314,6 +315,9 @@ void blk_cleanup_queue(struct request_queue *q)
 	 */
 	blk_freeze_queue(q);
 
+	/* cleanup rq qos structures for queue without disk */
+	rq_qos_exit(q);
+
 	blk_queue_flag_set(QUEUE_FLAG_DEAD, q);
 
 	blk_sync_queue(q);