[PATCH] block: fix updating bio's front segment size

[Ming Lei <ming.lei@redhat.com>]

When the current bvec can be merged to the 1st segment, the bio's front
segment size has to be updated.

However, dcebd755926b doesn't consider that case, then bio's front
segment size may not be correct.

This patch fixes this issue.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Omar Sandoval <osandov@fb.com>
Fixes: dcebd755926b ("block: use bio_for_each_bvec() to compute multi-page bvec count")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-merge.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 9402a7c3ba22..22467f475ab4 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -277,6 +277,9 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 			bvprvp = &bvprv;
 			sectors += bv.bv_len >> 9;
 
+			if (nsegs == 1 && seg_size > front_seg_size)
+				front_seg_size = seg_size;
+
 			continue;
 		}
 new_segment:
@@ -401,6 +404,11 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 
 				seg_size += bv.bv_len;
 				bvprv = bv;
+
+				if (nr_phys_segs == 1 && seg_size >
+						front_seg_size)
+					front_seg_size = seg_size;
+
 				continue;
 			}
 new_segment:
-- 
2.9.5