block: needs to set the residual length of a bidi request

Tejun's "block: set rq->resid_len to blk_rq_bytes() on issue" patch
seems to be incomplete; It doesn't set rq->resid_len to blk_rq_bytes()
for a bidi request (req->next_rq). As a result, all bidi users are
broken.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/blk-core.c

@@ -1846,6 +1846,9 @@ void blk_start_request(struct request *req)
 	 * resid_len to full count and add the timeout handler.
 	 */
 	req->resid_len = blk_rq_bytes(req);
+	if (unlikely(blk_bidi_rq(req)))
+		req->next_rq->resid_len = blk_rq_bytes(req->next_rq);
+
 	blk_add_timer(req);
 }
 EXPORT_SYMBOL(blk_start_request);