block: blk-merge: fix blk_recount_segments()

For cloned bio, bio->bi_vcnt can't be used at all, and we
have resort to bio_segments() to figure out how many
segment there are in the bio.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/blk-merge.c b/block/blk-merge.c
index b3ac40aef46b317c5a432a92ba9b40c8e1942504..89b97b5e0881853054c0807c5607c20d91d90762 100644 (file)
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -97,19 +97,22 @@ void blk_recalc_rq_segments(struct request *rq)
 
 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 {
-       bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
-                       &q->queue_flags);
-       bool merge_not_need = bio->bi_vcnt < queue_max_segments(q);
+       unsigned short seg_cnt;
+
+       /* estimate segment number by bi_vcnt for non-cloned bio */
+       if (bio_flagged(bio, BIO_CLONED))
+               seg_cnt = bio_segments(bio);
+       else
+               seg_cnt = bio->bi_vcnt;
 
-       if (no_sg_merge && !bio_flagged(bio, BIO_CLONED) &&
-                       merge_not_need)
-               bio->bi_phys_segments = bio->bi_vcnt;
+       if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
+                       (seg_cnt < queue_max_segments(q)))
+               bio->bi_phys_segments = seg_cnt;
        else {
                struct bio *nxt = bio->bi_next;
 
                bio->bi_next = NULL;
-               bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio,
-                               no_sg_merge && merge_not_need);
+               bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
                bio->bi_next = nxt;
        }