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From:   Ian Kumlien <ian.kumlien@gmail.com>
Date:   Wed, 5 Jul 2023 13:32:05 +0200
Message-ID: <CAA85sZsidN4ig=RaQ34PYFjnZGU-=zqR=r-5za=G4oeAtxDA7g@mail.gmail.com>
Subject: Re: [Intel-wired-lan] bug with rx-udp-gro-forwarding offloading?
To:     Paolo Abeni <pabeni@redhat.com>
Cc:     Alexander Lobakin <aleksander.lobakin@intel.com>,
        intel-wired-lan <intel-wired-lan@lists.osuosl.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Wed, Jul 5, 2023 at 12:28=E2=80=AFPM Paolo Abeni <pabeni@redhat.com> wro=
te:
>
> On Tue, 2023-07-04 at 16:27 +0200, Ian Kumlien wrote:
> > More stacktraces.. =3D)
> >
> > cat bug.txt | ./scripts/decode_stacktrace.sh vmlinux
> > [  411.413767] ------------[ cut here ]------------
> > [  411.413792] WARNING: CPU: 9 PID: 942 at include/net/ud     p.h:509
> > udpv6_queue_rcv_skb (./include/net/udp.h:509 net/ipv6/udp.c:800
> > net/ipv6/udp.c:787)
>
> I'm really running out of ideas here...
>
> This is:
>
>         WARN_ON_ONCE(UDP_SKB_CB(skb)->partial_cov);
>
> sort of hint skb being shared (skb->users > 1) while enqueued in
> multiple places (bridge local input and br forward/flood to tun
> device). I audited the bridge mc flooding code, and I could not find
> how a shared skb could land into the local input path.
>
> Anyway the other splats reported here and in later emails are
> compatible with shared skbs.
>
> The above leads to another bunch of questions:
> * can you reproduce the issue after disabling 'rx-gro-list' on the
> ingress device? (while keeping 'rx-udp-gro-forwarding' on).

With rx-gro-list off, as in never turned on, everything seems to run fine

> * do you have by chance qdiscs on top of the VM tun devices?

default qdisc is fq

> The last patch I shared was buggy, as it attempts to unclone the skb
> after already touching skb_shared_info.
>
> Could you please replace such patch with the following?

Will do, building atm

> Thanks!
>
> Paolo
> ---
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 6c5915efbc17..0b0f4309506d 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4261,6 +4261,17 @@ struct sk_buff *skb_segment_list(struct sk_buff *s=
kb,
>
>         skb_push(skb, -skb_network_offset(skb) + offset);
>
> +       if (WARN_ON_ONCE(skb_shared(skb))) {
> +               skb =3D skb_share_check(skb, GFP_ATOMIC);
> +               if (!skb)
> +                       goto err_linearize;
> +       }
> +
> +       /* later code will clear the gso area in the shared info */
> +       err =3D skb_unclone(skb, GFP_ATOMIC);
> +       if (err)
> +               goto err_linearize;
> +
>         skb_shinfo(skb)->frag_list =3D NULL;
>
>         while (list_skb) {
>