Re: [PATCH net 3/4] virtio-net: reset num_buf to 1 after linearizing packet

Michael S. Tsirkin
2018-05-21T14:59:18Z

On Mon, May 21, 2018 at 04:35:05PM +0800, Jason Wang wrote:
> If we successfully linearize the packets, num_buf were set to zero
> which was wrong since we now have only 1 buffer to be used for e.g in
> the error path of receive_mergeable(). Zero num_buf will lead the code
> try to pop the buffers of next packet and drop it. Fixing this by set
> num_buf to 1 if we successfully linearize the packet.
>
> Fixes: 4941d472bf95 ("virtio-net: do not reset during XDP set")
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
> drivers/net/virtio_net.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6260d65..165a922 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -722,6 +722,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> &len);
> if (!xdp_page)
> goto err_xdp;
> + num_buf = 1;

So this is tweaked here for the benefit of err_skb below.
That's confusing and we won't remember to change it
if we change the error handling.

How about fixing the error path?

- while (--num_buf) {
+ while (num_buf-- > 1) {

Seems more robust to me.

> offset = VIRTIO_XDP_HEADROOM;
> } else {
> xdp_page = page;
> --
> 2.7.4