dm: Ensure cloned bio is same length for atomic write

For an atomic write, a cloned bio must be same length as the original bio,
i.e. no splitting.

Error in case it is not.

Per-dm device queue limits should be setup to ensure that this does not
happen, but error this case as an insurance policy.

Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Author: johnpgarry

drivers/md/dm.c

@@ -1745,6 +1745,9 @@ static blk_status_t __split_and_process_bio(struct clone_info *ci)
 	ci->submit_as_polled = !!(ci->bio->bi_opf & REQ_POLLED);
 
 	len = min_t(sector_t, max_io_len(ti, ci->sector), ci->sector_count);
+	if (ci->bio->bi_opf & REQ_ATOMIC && len != ci->sector_count)
+		return BLK_STS_IOERR;
+
 	setup_split_accounting(ci, len);
 
 	if (unlikely(ci->bio->bi_opf & REQ_NOWAIT)) {