[PATCH] block: move sanity checking ahead of bi_front/back_seg_size updating

[Jianchao Wang]

If the bio_integrity_merge_rq() return false or nr_phys_segments exceeds
the max_segments, the merging fails, but the bi_front/back_seg_size may
have been modified. To avoid it, move the sanity checking ahead.

Signed-off-by: Jianchao Wang <jianchao.w.w...@oracle.com>
---
 block/blk-merge.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 99038830..14b6e37 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -553,6 +553,7 @@ static bool req_no_special_merge(struct request *req)
 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
                                struct request *next)
 {
+       bool contig;
        int total_phys_segments;
        unsigned int seg_size =
                req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
@@ -575,13 +576,9 @@ static int ll_merge_requests_fn(struct request_queue *q, 
struct request *req,
                return 0;
 
        total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
-       if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
-               if (req->nr_phys_segments == 1)
-                       req->bio->bi_seg_front_size = seg_size;
-               if (next->nr_phys_segments == 1)
-                       next->biotail->bi_seg_back_size = seg_size;
+       contig = blk_phys_contig_segment(q, req->biotail, next->bio);
+       if (contig)
                total_phys_segments--;
-       }
 
        if (total_phys_segments > queue_max_segments(q))
                return 0;
@@ -589,6 +586,13 @@ static int ll_merge_requests_fn(struct request_queue *q, 
struct request *req,
        if (blk_integrity_merge_rq(q, req, next) == false)
                return 0;
 
+       if (contig) {
+               if (req->nr_phys_segments == 1)
+                       req->bio->bi_seg_front_size = seg_size;
+               if (next->nr_phys_segments == 1)
+                       next->biotail->bi_seg_back_size = seg_size;
+       }
+
        /* Merge is OK... */
        req->nr_phys_segments = total_phys_segments;
        return 1;
-- 
2.7.4