[lvc-project] [PATCH] xen-netfront: handle NULL returned by xdp_convert_buff_to_frame()
Alexey
sdl at nppct.ru
Thu Apr 17 14:19:36 MSK 2025
On 17.04.2025 13:23, Jürgen Groß wrote:
> On 17.04.25 12:06, Alexey wrote:
>>
>> On 17.04.2025 11:51, Juergen Gross wrote:
>>> 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
>>
>> Agreed. There is no explicit freed pdata in the calling function
>> xennet_get_responses(). Without this, the page referenced by pdata
>> could be leaked.
>>
>> I suggest:
>
> Could you please merge the two if () blocks, as they share the
> call of xdp_return_frame_rx_napi() now? Something like:
>
> if (unlikely(err <= 0)) {
> if (err < 0)
> trace_xdp_exception(queue->info->netdev, prog, act);
> xdp_return_frame_rx_napi(xdpf);
> }
>
> Juergen
>
> P.S.: please don't use HTML in emails
I can't do this because xennet_xdp_xmit() can return a value > 0
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