block/mq-deadline: Add two lockdep_assert_held() statements

Document the locking strategy by adding two lockdep_assert_held()
statements.
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Cc: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20210618004456.7280-7-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/mq-deadline.c

@@ -279,6 +279,8 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd)
 	bool reads, writes;
 	int data_dir;
 
+	lockdep_assert_held(&dd->lock);
+
 	if (!list_empty(&dd->dispatch)) {
 		rq = list_first_entry(&dd->dispatch, struct request, queuelist);
 		list_del_init(&rq->queuelist);
@@ -501,6 +503,8 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
 	struct deadline_data *dd = q->elevator->elevator_data;
 	const int data_dir = rq_data_dir(rq);
 
+	lockdep_assert_held(&dd->lock);
+
 	/*
 	 * This may be a requeue of a write request that has locked its
 	 * target zone. If it is the case, this releases the zone lock.