Re: [PATCH] xen-netfront: handle NULL returned by xdp_convert_buff_to_frame()

[Juergen Gross]

On 17.04.25 10:45, Alexey wrote:
> On 17.04.2025 10:12, Jürgen Groß wrote:
> > On 17.04.25 09:00, Alexey wrote:
> > > On 17.04.2025 03:58, Jakub Kicinski wrote:
> > > > On Mon, 14 Apr 2025 18:34:01 +0000 Alexey Nepomnyashih wrote:
> > > > >           get_page(pdata);
> > > > Please notice this get_page() here.
> > > >
> > > > >           xdpf = xdp_convert_buff_to_frame(xdp);
> > > > > +        if (unlikely(!xdpf)) {
> > > > > +            trace_xdp_exception(queue->info->netdev, prog, act);
> > > > > +            break;
> > > > > +        }
> > > Do you mean that it would be better to move the get_page(pdata) call lower,
> > > after checking for NULL in xdpf, so that the reference count is only increased
> > > after a successful conversion?
> >
> > I think the error handling here is generally broken (or at least very
> > questionable).
> >
> > I suspect that in case of at least some errors the get_page() is leaking
> > even without this new patch.
> >
> > In case I'm wrong a comment reasoning why there is no leak should be
> > added.
> >
> >
> > Juergen
>
> I think pdata is freed in xdp_return_frame_rx_napi() -> __xdp_return()

Agreed. But what if xennet_xdp_xmit() returns an error < 0?

In this case xdp_return_frame_rx_napi() won't be called.


Juergen

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