Re: [Qemu-devel] [PATCH for-2.4] virtio-net: Flush incoming queues when DRIVER_OK is being set

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jul 14, 2015 at 05:41:04PM +0800, Fam Zheng wrote:
> This patch fixes network hang after "stop" then "cont", while network
> packets keep arriving.
> 
> Tested both manually (tap, host pinging guest) and with Jason's qtest
> series (plus his "[PATCH 2.4] socket: pass correct size in
> net_socket_send()" fix).
> 
> As virtio_net_set_status is called when guest driver is setting status
> byte and when vm state is changing, it is a good opportunity to flush
> queued packets.
> 
> This is necessary because during vm stop the backend (e.g. tap) would
> stop rx processing after .can_receive returns false, until the queue is
> explicitly flushed or purged.
> 
> The other interesting condition in .can_receive, virtio_queue_ready(),
> is handled by virtio_net_handle_rx() when guest kicks; the 3rd condition
> is invalid queue index which doesn't need flushing.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  hw/net/virtio-net.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index d728233..7c178c6 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -162,8 +162,13 @@ static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
>      virtio_net_vhost_status(n, status);
>  
>      for (i = 0; i < n->max_queues; i++) {
> +        NetClientState *ncs = qemu_get_subqueue(n->nic, i);
>          q = &n->vqs[i];
>  
> +        if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
> +            qemu_flush_queued_packets(ncs);
> +        }
> +
>          if ((!n->multiqueue && i != 0) || i >= n->curr_queues) {
>              queue_status = 0;
>          } else {

I think this should be limited to
	virtio_net_started(n, queue_status) && !n->vhost_started

> -- 
> 2.4.3