->bi_vcnt doesn't make sense for cloned bio, which is perfectly fine
passed to bio_may_need_split().

So fix bio_may_need_split() by not taking ->bi_vcnt directly, instead
checking with help from bio size and bvec->len.

Meantime retrieving the 1st bvec via __bvec_iter_bvec().

Fixes: abd45c159df5 ("block: handle fast path of bio splitting inline")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk.h | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/block/blk.h b/block/blk.h
index e4c433f62dfc..a0b9cecba8fa 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -371,12 +371,19 @@ struct bio *bio_split_zone_append(struct bio *bio,
 static inline bool bio_may_need_split(struct bio *bio,
 		const struct queue_limits *lim)
 {
+	const struct bio_vec *bv;
+
 	if (lim->chunk_sectors)
 		return true;
-	if (bio->bi_vcnt != 1)
+
+	if ((bio_op(bio) != REQ_OP_READ && bio_op(bio) != REQ_OP_WRITE) ||
+			!bio->bi_io_vec)
+		return true;
+
+	bv = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
+	if (bio->bi_iter.bi_size > bv->bv_len)
 		return true;
-	return bio->bi_io_vec->bv_len + bio->bi_io_vec->bv_offset >
-		lim->max_fast_segment_size;
+	return bv->bv_len + bv->bv_offset > lim->max_fast_segment_size;
 }
 
 /**
-- 
2.47.0