[PATCH] bio: decrease bi_iter.bi_size by len in the fail path

[Dongsu Park <dongsu.park@profitbricks.com>]

From: Dongsu Park <dongsu.park@profitbricks.com>

Commit 3979ef4dcf3d1de55a560a3a4016c30a835df44d ("bio-modify-
__bio_add_page-to-accept-pages-that-dont-start-a-new-segment-v3")
introduced a regression as reported by Jet Chen.
That results in a kernel BUG at drivers/block/virtio_blk.c:166.

To fix that, bi_iter.bi_size must be decreased by len, before
recounting the number of physical segments.

Tested on with kernel 3.15.0-rc7-next-20140527 on qemu guest,
by running xfstests/ext4/271.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jet Chen <jet.chen@intel.com>
Cc: Maurizio Lombardi <mlombard@redhat.com>
Signed-off-by: Dongsu Park <dongsu.park@profitbricks.com>
---
 block/bio.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/bio.c b/block/bio.c
index 0443694ccbb4..67d7cba1e5fd 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -810,6 +810,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
 	bvec->bv_len = 0;
 	bvec->bv_offset = 0;
 	bio->bi_vcnt--;
+	bio->bi_iter.bi_size -= len;
 	blk_recount_segments(q, bio);
 	return 0;
 }
-- 
1.9.1