dm raid: fix false positive for requeue needed during reshape

An empty flush doesn't have a payload, so it should never be looked at
when considering to possibly requeue a bio for the case when a reshape
is in progress.

Fixes: 9dbd1aa3 ("dm raid: add reshaping support to the target")
Reported-by: Patrick Plenefisch <simonpatp@gmail.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm-raid.c

@@ -3329,14 +3329,14 @@ static int raid_map(struct dm_target *ti, struct bio *bio)
 	struct mddev *mddev = &rs->md;
 
 	/*
-	 * If we're reshaping to add disk(s)), ti->len and
+	 * If we're reshaping to add disk(s), ti->len and
 	 * mddev->array_sectors will differ during the process
 	 * (ti->len > mddev->array_sectors), so we have to requeue
 	 * bios with addresses > mddev->array_sectors here or
 	 * there will occur accesses past EOD of the component
 	 * data images thus erroring the raid set.
 	 */
-	if (unlikely(bio_end_sector(bio) > mddev->array_sectors))
+	if (unlikely(bio_has_data(bio) && bio_end_sector(bio) > mddev->array_sectors))
 		return DM_MAPIO_REQUEUE;
 
 	md_handle_request(mddev, bio);