[Qemu-devel] [PATCH 3/3] virtio-net: purge outstanding packets when starting vhost

["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>
---
 hw/net/virtio-net.c | 15 ++++++++++++++-
 net/net.c           |  1 +
 2 files changed, 15 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) {
diff --git a/net/net.c b/net/net.c
index 25fdb07..b94473e 100644
--- a/net/net.c
+++ b/net/net.c
@@ -41,6 +41,7 @@
 #include "qapi-visit.h"
 #include "qapi/opts-visitor.h"
 #include "qapi/dealloc-visitor.h"
+#include "sysemu/sysemu.h"
 
 /* Net bridge is currently not supported for W32. */
 #if !defined(_WIN32)
-- 
MST