[PATCH] vhost: fix avail idx update error when desc copy failed

[Gaoxiang Liu <gaoxiangliu0@163.com>]

When copy_desc_to_mbuf function failed, i added 1.
And last_avail_idx added i, other than i - 1.
It may cause that the first mbuf in mbuf-list is dropped,
the second mbuf in mbuf-list is received in the following
rx procedure.
And The pkt_len of the second mbuf is zero, resulting in
segment fault when parsing the mbuf.

Fixes: 0fd5608ef97f ("vhost: handle mbuf allocation failure")
Cc: stable@dpdk.org

Signed-off-by: Gaoxiang Liu <liugaoxiang@huawei.com>
---
 lib/vhost/virtio_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
index 68a26eb17d..86f1c04b43 100644
--- a/lib/vhost/virtio_net.c
+++ b/lib/vhost/virtio_net.c
@@ -2850,7 +2850,7 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	if (dropped)
 		rte_pktmbuf_free_bulk(&pkts[i - 1], count - i + 1);
 
-	vq->last_avail_idx += i;
+	vq->last_avail_idx += i - 1;
 
 	do_data_copy_dequeue(vq);
 	if (unlikely(i < count))
-- 
2.32.0