[PATCH] block: return the correct bvec when checking for gaps

[longli@linuxonhyperv.com]

From: Long Li <longli@microsoft.com>

After commit 07173c3ec276 ("block: enable multipage bvecs"), a bvec can
have multiple pages. But bio_will_gap() still assumes one page bvec while
checking for merging. This causes data corruption on drivers relying on
the correct merging on virt_boundary_mask.

Fix this by returning the multi-page bvec for testing gaps for merging.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Jeffle Xu <jefflexu@linux.alibaba.com>
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: 07173c3ec276 ("block: enable multipage bvecs")
Signed-off-by: Long Li <longli@microsoft.com>
---
 include/linux/bio.h | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/include/linux/bio.h b/include/linux/bio.h
index a0b4cfdf62a4..6b2f609ccfbf 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -44,9 +44,6 @@ static inline unsigned int bio_max_segs(unsigned int nr_segs)
 #define bio_offset(bio)		bio_iter_offset((bio), (bio)->bi_iter)
 #define bio_iovec(bio)		bio_iter_iovec((bio), (bio)->bi_iter)
 
-#define bio_multiple_segments(bio)				\
-	((bio)->bi_iter.bi_size != bio_iovec(bio).bv_len)
-
 #define bvec_iter_sectors(iter)	((iter).bi_size >> 9)
 #define bvec_iter_end_sector(iter) ((iter).bi_sector + bvec_iter_sectors((iter)))
 
@@ -271,7 +268,7 @@ static inline void bio_clear_flag(struct bio *bio, unsigned int bit)
 
 static inline void bio_get_first_bvec(struct bio *bio, struct bio_vec *bv)
 {
-	*bv = bio_iovec(bio);
+	*bv = mp_bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
 }
 
 static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
@@ -279,10 +276,10 @@ static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
 	struct bvec_iter iter = bio->bi_iter;
 	int idx;
 
-	if (unlikely(!bio_multiple_segments(bio))) {
-		*bv = bio_iovec(bio);
+	/* this bio has only one bvec */
+	*bv = mp_bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
+	if (bv->bv_len == bio->bi_iter.bi_size)
 		return;
-	}
 
 	bio_advance_iter(bio, &iter, iter.bi_size);
 
-- 
2.17.1