Re: [PATCH net] xsk: defer software checksum until the skb is complete

[王荣峥]

Hi,

I found this while studying the AF_XDP kernel implementation and running my
own multi-buffer TX tests. When I enabled XDP_UMEM_TX_SW_CSUM and sent a UDP
packet as two descriptors, the checksum on the wire did not match the
expected value; the same packet as a single descriptor was correct. I then
traced it to xsk_skb_metadata() calling skb_checksum_help() before the
remaining fragments were added.

This was not a production or syzbot report. I reproduced it with a standalone
AF_XDP TAP test and extended the kernel selftest: the unpatched kernel gives
actual 8817 vs expected 52507, while the patched kernel gives the same
correct checksum for both single- and multi-buffer TX.

Thanks,
Rongzheng


<netdev-bot+sinfo@xxxxxxxxxx> 于2026年10月24日周六 17:15写道：
>
> Hi!
>
> This is an automated message. This series looks like a fix, but its
> commit messages seem to be missing some information:
>
>  - How the issue was discovered, e.g. hit in production, hit during
>    development, syzbot report, manual code inspection, LLM or static
>    analysis tool scan.
>
> Please do not repost the series just to address the above. Instead,
> reply to this email with the missing information, so that reviewers
> can take it into account. If the series needs another revision for
> other reasons, please include the information in the commit messages
> then.
>
> The evaluation is done by an LLM so it may be wrong, if you think
> that is the case please reply and explain.