[Qemu-devel] [PULL 7/7] virtio-net: purge outstanding packets when starting vhost

[Stefan Hajnoczi <stefanha@redhat.com>]

From: "Michael S. Tsirkin" <mst@redhat.com>

whenever we start vhost, virtio could have outstanding packets
queued, when they complete later we'll modify the ring
while vhost is processing it.

To prevent this, purge outstanding packets on vhost start.

Cc: qemu-stable@nongnu.org
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/net/virtio-net.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 365e266..826a2a5 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -125,10 +125,23 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t status)
         return;
     }
     if (!n->vhost_started) {
-        int r;
+        int r, i;
+
         if (!vhost_net_query(get_vhost_net(nc->peer), vdev)) {
             return;
         }
+
+        /* Any packets outstanding? Purge them to avoid touching rings
+         * when vhost is running.
+         */
+        for (i = 0;  i < queues; i++) {
+            NetClientState *qnc = qemu_get_subqueue(n->nic, i);
+
+            /* Purge both directions: TX and RX. */
+            qemu_net_queue_purge(qnc->peer->incoming_queue, qnc);
+            qemu_net_queue_purge(qnc->incoming_queue, qnc->peer);
+        }
+
         n->vhost_started = 1;
         r = vhost_net_start(vdev, n->nic->ncs, queues);
         if (r < 0) {
-- 
1.9.3