[Devel] [PATCH vz9] dm-qcow2: only use inline bvec if iteration is valid

[Alexander Atanasov]

In some cases qcow2 is passed requests without bvec set and
zero bi_size - for such requests qcow2 resorts to inline bvecs
which in that case are invalid.

To address this:
- Check if bi_size is not zero, and only then use the inline bvecs.
- Properly count number of segments in a NULL bvec.
- Add warn on to catch if we have a requests without bvec and bi_size.

https://virtuozzo.atlassian.net/browse/PSBM-159903
Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
---
 drivers/md/dm-qcow2-map.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
index 6585f3fac6e7..a28f6332dc08 100644
--- a/drivers/md/dm-qcow2-map.c
+++ b/drivers/md/dm-qcow2-map.c
@@ -308,6 +308,9 @@ static unsigned int qio_nr_segs(struct qio *qio)
 	struct bvec_iter iter;
 	struct bio_vec bv;
 
+	if (!qio->bi_io_vec)
+		return nr_segs;
+
 	qcow2_for_each_bvec(iter, bv, qio->bi_iter, qio->bi_io_vec)
 		nr_segs++;
 
@@ -1248,6 +1251,7 @@ static void __submit_rw_mapped(struct qcow2 *qcow2, struct qio *qio, u32 nr_segs
 	bvec = __bvec_iter_bvec(qio->bi_io_vec, qio->bi_iter);
 	pos = to_bytes(qio->bi_iter.bi_sector);
 
+	WARN_ON(qio->bi_iter.bi_size && !bvec);
 	iov_iter_bvec(&iter, rw, bvec, nr_segs, qio->bi_iter.bi_size);
 	iter.iov_offset = qio->bi_iter.bi_bvec_done;
 
@@ -3538,7 +3542,7 @@ static void prepare_one_embedded_qio(struct qcow2 *qcow2, struct qio *qio,
 	} else {
 		/* Single bio already provides bvec array */
 		bvec = rq->bio->bi_io_vec;
-		if (!bvec) {
+		if (!bvec && rq->bio->bi_iter.bi_size) {
 			bvec = rq->bio->bi_inline_vecs;
 			if (unlikely(!bvec)) {
 				QC_ERR(qcow2->tgt->ti, "Expecting inline bvec");
-- 
2.43.0