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

[Jason Wang]

On 2018å05æ21æ 22:59, Michael S. Tsirkin wrote:
> 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@xxxxxxxxxx>
> > ---
> >   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.

Looks good, will do this in V2.

Thanks

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