netdev - Re: null pointer dereference in interrupt after receiving an ip packet on veth from xsk from user space

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Message-ID: <CAL+tcoDqgQbs20xV34RFWDoE5YPXS-ne3FBns2n9t4eggx8LAQ@mail.gmail.com>
Date: Mon, 20 Oct 2025 17:04:15 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: mc36 <csmate@....hu>
Cc: Jonathan Lemon <jonathan.lemon@...il.com>, Stanislav Fomichev <sdf@...ichev.me>, 
	Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Magnus Karlsson <magnus.karlsson@...el.com>, 
	Björn Töpel <bjorn@...nel.org>, 1118437@...s.debian.org, 
	netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: null pointer dereference in interrupt after receiving an ip
 packet on veth from xsk from user space

On Mon, Oct 20, 2025 at 4:55 PM mc36 <csmate@....hu> wrote:
>
> hi,
>
> On 10/20/25 08:41, Jason Xing wrote:
> > Hi,
> >
> >> this happens 10/10 on host or in qemu-system-x86_64-kvm running 6.16.12 or 6.17.2...
> >
> > Thanks for the report.
> >
> > I'm wondering if you have time to bisect which recent commit has
> > brought this problem. It looks like it never happens before 6.16?
> >
>
> and now confirming that 6.16.7 survives the reproducer code and 6.16.8 crashes...
>
> below is the decoded and raw 6.17 trace... regarding the exact commit hash, i
>
> would leave the chance for someone with much more resources than i have at hand....

Thanks for working on this.

Strange thing is that I didn't manage to see the crash on 6.16.0-rc6,
6.17.0-rc3 or 6.18.0-rc1 that is the latest. I feel that your
environment is hugely different from mine.

I followed your steps you attached in your code:
////// gcc xskInt.c -lxdp
////// sudo ip link add veth1 type veth
////// sudo ip link set veth0 up
////// sudo ip link set veth1 up
////// sudo ./a.out

The version of libxdp that I use is 1.4.2, BTW.

Could you share me with your .config? I'm not sure if I missed something.

Thanks,
Jason