netdev - Re: tcp: kernel BUG at net/core/skbuff.c:3574!

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Message-ID: <9e394d57ada54c604fca2a6798b1a4da3921874c.camel@redhat.com>
Date:   Tue, 21 Dec 2021 19:13:27 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Ignat Korchagin <ignat@...udflare.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        kernel-team <kernel-team@...udflare.com>
Subject: Re: tcp: kernel BUG at net/core/skbuff.c:3574!

On Tue, 2021-12-21 at 18:01 +0000, Ignat Korchagin wrote:
> On Tue, Dec 21, 2021 at 5:31 PM Paolo Abeni <pabeni@...hat.com> wrote:
> > 
> > On Tue, 2021-12-21 at 17:16 +0000, Ignat Korchagin wrote:
> > > On Tue, Dec 21, 2021 at 3:40 PM Paolo Abeni <pabeni@...hat.com> wrote:
> > > > 
> > > > On Tue, 2021-12-21 at 06:16 -0800, Eric Dumazet wrote:
> > > > > On Tue, Dec 21, 2021 at 4:19 AM Ignat Korchagin <ignat@...udflare.com> wrote:
> > > > > > 
> > > > > > Hi netdev,
> > > > > > 
> > > > > > While trying to reproduce a different rare bug we're seeing in
> > > > > > production I've triggered below on 5.15.9 kernel and confirmed on the
> > > > > > latest netdev master tree:
> > > > > > 
> > > > > 
> > > > > Nothing comes to mind. skb_shift() has not been recently changed.
> > > > > 
> > > > > Why are you disabling TSO exactly ?
> > > > > 
> > > > > Is GRO being used on veth needed to trigger the bug ?
> > > > > (GRO was added recently to veth, I confess I did not review the patches)
> > > 
> > > Yes, it seems enabling GRO for veth actually enables NAPI codepaths,
> > > which trigger this bug (and actually another one we're investigating).
> > > Through trial-and-error it seems disabling TSO is more likely to
> > > trigger it at least in my dev environment. I'm not sure if this bug is
> > > somehow related to the other one we're investigating, but once we have
> > > a fix here I can try to verify before posting it to the mailing list.
> > > 
> > > > This is very likely my fault. I'm investigating it right now.
> > > 
> > > Thank you very much! Let me know if I can help somehow.
> > 
> > I'm testing the following patch. Could you please have a spin in your
> > testbed, too?
> 
> Seems with the patch the BUG does not reproduce for me anymore.

Thank you for testing. I'll submit that formally after some more
testing on my side.

Thanks!

Paolo