block/mq-deadline: Fix a bug in deadline_from_pos()

A bug was introduced in deadline_from_pos() while implementing the
suggestion to use round_down() in the following code:

	pos -= bdev_offset_from_zone_start(rq->q->disk->part0, pos);

This patch makes deadline_from_pos() use round_down() such that 'pos' is
rounded down.

Reported-by: Shin'ichiro Kawasaki <[email protected]>
Closes: https://lore.kernel.org/all/5zthzi3lppvcdp4nemum6qck4gpqbdhvgy4k3qwguhgzxc4quj@amulvgycq67h/
Cc: Christoph Hellwig <[email protected]>
Cc: Damien Le Moal <[email protected]>
Fixes: 0effb39 ("block: mq-deadline: Handle requeued requests correctly")
Signed-off-by: Bart Van Assche <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: bvanassche

block/mq-deadline.c

@@ -176,7 +176,7 @@ static inline struct request *deadline_from_pos(struct dd_per_prio *per_prio,
 	 * zoned writes, start searching from the start of a zone.
 	 */
 	if (blk_rq_is_seq_zoned_write(rq))
-		pos -= round_down(pos, rq->q->limits.chunk_sectors);
+		pos = round_down(pos, rq->q->limits.chunk_sectors);
 
 	while (node) {
 		rq = rb_entry_rq(node);