[PATCH] md: fix splitting of md/linear request that cross a device boundary

When a request crosses a boundary between devices, it needs to be split.
But where we should calculate the amount of the request before the boundary
to find the split-point, we care currently calculating the amount that is
*after* the boundary !!!
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/md/linear.c

@@ -269,9 +269,8 @@ static int linear_make_request (request_queue_t *q, struct bio *bio)
 		 * split it.
 		 */
 		struct bio_pair *bp;
-		bp = bio_split(bio, bio_split_pool, 
-			       (bio->bi_sector + (bio->bi_size >> 9) -
-				(tmp_dev->offset + tmp_dev->size))<<1);
+		bp = bio_split(bio, bio_split_pool,
+			       ((tmp_dev->offset + tmp_dev->size)<<1) - bio->bi_sector);
 		if (linear_make_request(q, &bp->bio1))
 			generic_make_request(&bp->bio1);
 		if (linear_make_request(q, &bp->bio2))