[PATCH V10 17/19] block: don't use bio->bi_vcnt to figure out segment number

[Ming Lei]

It is wrong to use bio->bi_vcnt to figure out how many segments
there are in the bio even though CLONED flag isn't set on this bio,
because this bio may be splitted or advanced.

So always use bio_segments() in blk_recount_segments(), and it shouldn't
cause any performance loss now because the physical segment number is figured
out in blk_queue_split() and BIO_SEG_VALID is set meantime since
bdced438acd83ad83a6c ("block: setup bi_phys_segments after splitting").

Cc: Dave Chinner <dchinner at redhat.com>
Cc: Kent Overstreet <kent.overstreet at gmail.com>
Fixes: 7f60dcaaf91 ("block: blk-merge: fix blk_recount_segments()")
Cc: Mike Snitzer <snitzer at redhat.com>
Cc: dm-devel at redhat.com
Cc: Alexander Viro <viro at zeniv.linux.org.uk>
Cc: linux-fsdevel at vger.kernel.org
Cc: Shaohua Li <shli at kernel.org>
Cc: linux-raid at vger.kernel.org
Cc: linux-erofs at lists.ozlabs.org
Cc: David Sterba <dsterba at suse.com>
Cc: linux-btrfs at vger.kernel.org
Cc: Darrick J. Wong <darrick.wong at oracle.com>
Cc: linux-xfs at vger.kernel.org
Cc: Gao Xiang <gaoxiang25 at huawei.com>
Cc: Christoph Hellwig <hch at lst.de>
Cc: Theodore Ts'o <tytso at mit.edu>
Cc: linux-ext4 at vger.kernel.org
Cc: Coly Li <colyli at suse.de>
Cc: linux-bcache at vger.kernel.org
Cc: Boaz Harrosh <ooo at electrozaur.com>
Cc: Bob Peterson <rpeterso at redhat.com>
Cc: cluster-devel at redhat.com
Signed-off-by: Ming Lei <ming.lei at redhat.com>
---
 block/blk-merge.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index cb9f49bcfd36..153a659fde74 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -429,13 +429,7 @@ void blk_recalc_rq_segments(struct request *rq)
 
 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 {
-	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;
+	unsigned short seg_cnt = bio_segments(bio);
 
 	if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 			(seg_cnt < queue_max_segments(q)))
-- 
2.9.5