linux-kernel - Re: 4.20-rc6: WARNING: CPU: 30 PID: 197360 at net/core/flow_dissector.c:764 __skb_flow

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Date:   Fri, 21 Dec 2018 09:42:36 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Ido Schimmel <idosch@...sch.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Michael S Tsirkin <mst@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: 4.20-rc6: WARNING: CPU: 30 PID: 197360 at net/core/flow_dissector.c:764
 __skb_flow_dissect

On Fri, Dec 21, 2018 at 1:45 AM Christian Borntraeger
<borntraeger@...ibm.com> wrote:
>
>
>
> On 20.12.2018 18:23, Willem de Bruijn wrote:
> > On Thu, Dec 20, 2018 at 11:17 AM Ido Schimmel <idosch@...sch.org> wrote:
> >>
> >> On Thu, Dec 20, 2018 at 03:09:22PM +0100, Christian Borntraeger wrote:
> >>> On 20.12.2018 10:12, Ido Schimmel wrote:
> >>>> +Willem
> >>>>
> >>>> On Thu, Dec 20, 2018 at 08:45:40AM +0100, Christian Borntraeger wrote:
> >>>>> Folks,
> >>>>>
> >>>>> I got this warning today. I cant tell when and why this happened, so I do not know yet how to reproduce.
> >>>>> Maybe someone has a quick idea.
> >>>>>
> >>>>> [85109.572032] WARNING: CPU: 30 PID: 197360 at net/core/flow_dissector.c:764 __skb_flow_dissect+0x1f0/0x1318
> >>>>
> >>>> I managed to trigger this warning as well the other day, but from a
> >>>> different call path:
> >>>
> >>> FWIW, it also seems to happen on 4.20-rc1. 4.19.0 seems fine. bisect seem to have failed so
> >>> my reproducer is not reliable.
> >>
> >> Yes, it is caused by commit d0e13a1488ad ("flow_dissector: lookup netns
> >> by skb->sk if skb->dev is NULL")
> >>
> >> $ git tag --contains d0e13a1488ad
> >> v4.20-rc1
> >> v4.20-rc2
> >> v4.20-rc3
> >> v4.20-rc4
> >> v4.20-rc5
> >> v4.20-rc6
> >
> > That tap_get_user_xdp path is also new for 4.20-rc1:
> >
> >     commit 0efac27791ee068075d80f07c55a229b1335ce12
> >     tap: accept an array of XDP buffs through sendmsg()
> >
> >     $ git describe --contains 0efac27791ee
> >     v4.20-rc1~14^2~382^2~1
> >
> > In v4.19 and before all packets went through tap_get_user.
>
> Hmmm, so maybe my bisect wasnt broken at all? It pointed to
>
> commit 105bc1306e9b29c2aa2783b9524f7aec9b5a5b1f
> Merge: 3475372ff60e4 d0e13a1488ad3
> Author:     David S. Miller <davem@...emloft.net>
> AuthorDate: Tue Sep 25 20:29:38 2018 -0700
> Commit:     David S. Miller <davem@...emloft.net>
> CommitDate: Tue Sep 25 20:29:38 2018 -0700
>
>     Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next

Yes, that's the right commit. The flow dissector change went in
through bpf-next.