virtio_net: doesn't free last skb in tx buffer

Hi,

I have been chasing a fault when closing a network namespace with a soft device in (vlan, macvlan, ...) and the "real" device is a virtio device. I couldn't decide if I should email the netdev or virtualization list but I hope it is sent right.

The problem is that the namespace can never close because there is a neighbour entry holding a reference to the device. This neighbour entry is not free:d since a dst_entry is left with a reference to it and this dst_entry is referenced from the last sk_buff sent on the virtio device.

From the code it looks like whenever a sk_buff should be sent in the start_xmit (driver/net/virtio_net.c) function the driver checks the tx ring buffer if there are any old sk_buff there that should be free:d. When the network namespace is closed down the last sk_buff cannot be free:d until another is sent and if this doesn't happen the namespace will hang forever.

Now this could be done in the net_device_ops ndo_uninit, but it seems like if the there is a device on top of the virtio device, e.g. a vlan device, the ndo_uninit is called for the vlan but the vlan never passes it down to the real_dev. The same can be seen in the macvlan driver as well. Is it made like this intentional and in that case what is the preferred way for a device driver to clean up stuff during network namespace shutdown?

Wouldn't this cause a more generic problem for network device drivers that expect to be able to clean up stuff in ndo_uninit or is this not meant to be used for this and the problem is specific to the virtio_net leaving data after start_xmit returns?

BR,
--Daniel