bio: ensure __bio_clone_fast copies bi_partno

A new field was introduced in 74d46992, bi_partno, instead of using
bdev->bd_contains and encoding the partition information in the bi_bdev
field.  __bio_clone_fast was changed to copy the disk information, but
not the partition information.  At minimum, this regressed bcache and
caused data corruption.
Signed-off-by: Michael Lyle <mlyle@lyle.org>
Fixes: 74d46992 ("block: replace bi_bdev with a gendisk pointer and partitions index")
Reported-by: Pavel Goran <via-bcache@pvgoran.name>
Reported-by: Campbell Steven <casteven@gmail.com>
Reviewed-by: Coly Li <colyli@suse.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Cc: <stable@vger.kernel.org> # 4.14
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -597,6 +597,7 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src)
 	 * so we don't set nor calculate new physical/hw segment counts here
 	 */
 	bio->bi_disk = bio_src->bi_disk;
+	bio->bi_partno = bio_src->bi_partno;
 	bio_set_flag(bio, BIO_CLONED);
 	bio->bi_opf = bio_src->bi_opf;
 	bio->bi_write_hint = bio_src->bi_write_hint;