[PATH 2/2] vhost: fix slot index calculation in async vhost

[Cheng Jiang]

When the packet receiving failure and the DMA ring full occur
simultaneously in the asynchronous vhost, the slot_idx needs to be
reduced by 1. For packed virtqueue, the slot index should be
ring_size - 1, if the slot_idx is currently 0, since the ring size is
not necessarily the power of 2.

Signed-off-by: Cheng Jiang <cheng1.ji...@intel.com>
---
 lib/vhost/virtio_net.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
index bfc6d65b7c..f804bce0bd 100644
--- a/lib/vhost/virtio_net.c
+++ b/lib/vhost/virtio_net.c
@@ -3462,6 +3462,7 @@ virtio_dev_tx_async_split(struct virtio_net *dev, struct 
vhost_virtqueue *vq,
                                allocerr_warned = true;
                        }
                        dropped = true;
+                       slot_idx--;
                        break;
                }
 
@@ -3652,6 +3653,12 @@ virtio_dev_tx_async_packed(struct virtio_net *dev, 
struct vhost_virtqueue *vq,
                if (unlikely(virtio_dev_tx_async_single_packed(dev, vq, 
mbuf_pool, pkt,
                                slot_idx, legacy_ol_flags))) {
                        rte_pktmbuf_free_bulk(&pkts_prealloc[pkt_idx], count - 
pkt_idx);
+
+                       if (slot_idx == 0)
+                               slot_idx = vq->size - 1;
+                       else
+                               slot_idx--;
+
                        break;
                }
 
@@ -3679,8 +3686,13 @@ virtio_dev_tx_async_packed(struct virtio_net *dev, 
struct vhost_virtqueue *vq,
                        async->buffer_idx_packed += vq->size - pkt_err;
 
                while (pkt_err-- > 0) {
-                       rte_pktmbuf_free(pkts_info[slot_idx % vq->size].mbuf);
-                       slot_idx--;
+                       rte_pktmbuf_free(pkts_info[slot_idx].mbuf);
+                       descs_err += pkts_info[slot_idx].descs;
+
+                       if (slot_idx == 0)
+                               slot_idx = vq->size - 1;
+                       else
+                               slot_idx--;
                }
 
                /* recover available ring */
-- 
2.35.1