diff --git a/include/linux/bio.h b/include/linux/bio.h
index ec4db73e5f4e..20ccf5796ea0 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -286,6 +286,7 @@ static inline void bio_first_folio(struct folio_iter *fi, struct bio *bio,
 {
 	struct bio_vec *bvec = bio_first_bvec_all(bio) + i;
 
+	WARN_ON_ONCE(!bio->bi_vcnt);
 	fi->folio = page_folio(bvec->bv_page);
 	fi->offset = bvec->bv_offset +
 			PAGE_SIZE * (bvec->bv_page - &fi->folio->page);
diff --git a/block/blk-map.c b/block/blk-map.c
index 8584babf3ea0..e2169d67be4b 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -275,6 +275,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 	if (!iov_iter_count(iter))
 		return -EINVAL;
 
+	printk("i: %p, nr: %d, cn: %lld, %s\n", iter, nr_vecs, iov_iter_count(iter), __func__);
 	bio = blk_rq_map_bio_alloc(rq, nr_vecs, gfp_mask);
 	if (bio == NULL)
 		return -ENOMEM;
@@ -298,6 +299,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 					       nr_vecs, extraction_flags, &offs);
 		if (unlikely(bytes <= 0)) {
 			ret = bytes ? bytes : -EFAULT;
+			printk("r: %d, b: %lld, icn: %d, %s\n", ret, bytes, iov_iter_count(iter), __func__);
 			goto out_unmap;
 		}
 
@@ -339,6 +341,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 	}
 
 	ret = blk_rq_append_bio(rq, bio);
+	printk("b: %p, r: %d, %s\n", bio, ret, __func__);
 	if (ret)
 		goto out_unmap;
 	return 0;