Thanks so much for your suggestion! I just submitted the v2 based on
your comments for this issue :)
On Fri, Jul 25, 2025 at 5:39 AM Kunwu Chan <kunwu.chan@xxxxxxxxx> wrote:
>
> On 2025/7/25 18:11, Edward Cree wrote:
> > On 7/24/25 10:57, Paolo Abeni wrote:
> >> On 7/23/25 2:32 AM, Chenyuan Yang wrote:
> >>> The xdp_convert_buff_to_frame() function can return NULL when there is
> >>> insufficient headroom in the buffer to store the xdp_frame structure
> >>> or when the driver didn't reserve enough tailroom for skb_shared_info.
> >> AFAIC the sfc driver reserves both enough headroom and tailroom, but
> >> this is after ebpf run, which in turn could consume enough headroom to
> >> cause a failure, so I think this makes sense.
> > Your reasoning seems plausible to me.
> > However, I think the error path ought to more closely follow the existing
> > error cases in logging a ratelimited message and calling the tracepoint.
> > I think the cleanest way to do this would be:
> > if (unlikely(!xdpf))
> > err = -ENOBUFS;
> > else
> > err = efx_xdp_tx_buffers(efx, 1, &xdpf, true);
> > so that it can make use of the existing failure path.
> > Adding the check to efx_xdp_tx_buffers() is also an option.
> >
> > -ed
> >
> Hi Chenyuan,
>
> THX for addressing this edge case. I concur with Edward's suggestion to
> integrate this with the existing error handling flow. This will ensure:
> Consistent observability (ratelimited logs + tracepoints)
> Centralized resource cleanup
> Clear error type differentiation via -ENOBUFS
>
> Proposed refinement:
>
> diff
> case XDP_TX:
> /* Buffer ownership passes to tx on success. */
> xdpf = xdp_convert_buff_to_frame(&xdp);
> + if (unlikely(!xdpf)) {
> + err = -ENOBUFS;
> + } else {
> + err = efx_siena_xdp_tx_buffers(efx, 1, &xdpf, true);
> + }
>
> - err = efx_siena_xdp_tx_buffers(efx, 1, &xdpf, true);
> if (unlikely(err != 1)) {
> efx_siena_free_rx_buffers(rx_queue, rx_buf, 1);
> if (net_ratelimit())
> netif_err(efx, rx_err, efx->net_dev,
> - "XDP TX failed (%d)\n", err);
> + "XDP TX failed (%d)%s\n", err,
> + err == -ENOBUFS ? " [frame conversion]" : "");
> channel->n_rx_xdp_bad_drops++;
> - trace_xdp_exception(efx->net_dev, xdp_prog, xdp_act);
> + if (err != -ENOBUFS)
> + trace_xdp_exception(efx->net_dev, xdp_prog, xdp_act);
> } else {
> channel->n_rx_xdp_tx++;
> }
> break;
>
>
> -- Thanks, TAO. --- “Life finds a way.”
