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

Juergen Gross
2025-04-17T08:51:20Z

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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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