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

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Message-ID: <CAF=yD-KBkX3NxtDt6mv-PoujFfdtJJ66XsnGzx-KQop6EU6LRw@mail.gmail.com>
Date:   Thu, 20 Dec 2018 12:23:39 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        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 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.