4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ming Lei <ming....@canonical.com>

commit 25e71a99f10e444cd00bb2ebccb11e1c9fb672b1 upstream.

This patch applies the two introduced helpers to
figure out the 1st and last bvec, and fixes the
original way after bio splitting.

Reported-by: Sagi Grimberg <sa...@dev.mellanox.co.il>
Reviewed-by: Sagi Grimberg <sa...@mellanox.com>
Reviewed-by: Christoph Hellwig <h...@lst.de>
Signed-off-by: Ming Lei <ming....@canonical.com>
Signed-off-by: Jens Axboe <ax...@fb.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 include/linux/blkdev.h |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1389,11 +1389,16 @@ static inline bool bvec_gap_to_prev(stru
 static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
                         struct bio *next)
 {
-       if (!bio_has_data(prev) || !queue_virt_boundary(q))
-               return false;
+       if (bio_has_data(prev) && queue_virt_boundary(q)) {
+               struct bio_vec pb, nb;
 
-       return __bvec_gap_to_prev(q, &prev->bi_io_vec[prev->bi_vcnt - 1],
-                                 next->bi_io_vec[0].bv_offset);
+               bio_get_last_bvec(prev, &pb);
+               bio_get_first_bvec(next, &nb);
+
+               return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
+       }
+
+       return false;
 }
 
 static inline bool req_gap_back_merge(struct request *req, struct bio *bio)


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