Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <c4e40b45b41d0476afd8989d31e6bab74c51a72a.camel@redhat.com>
Subject: Re: [Intel-wired-lan] bug with rx-udp-gro-forwarding offloading?
From:   Paolo Abeni <pabeni@redhat.com>
To:     Eric Dumazet <edumazet@google.com>,
        Willem de Bruijn <willemb@google.com>
Cc:     Ian Kumlien <ian.kumlien@gmail.com>,
        Alexander Lobakin <aleksander.lobakin@intel.com>,
        intel-wired-lan <intel-wired-lan@lists.osuosl.org>,
        Jakub Kicinski <kuba@kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Date:   Thu, 06 Jul 2023 16:04:23 +0200
In-Reply-To: <CANn89i+F=R71refT8K_8hPaP+uWn15GeHz+FTMYU=VPTG24WFA@mail.gmail.com>
References: <CAA85sZukiFq4A+b9+en_G85eVDNXMQsnGc4o-4NZ9SfWKqaULA@mail.gmail.com>
         <CAA85sZvm1dL3oGO85k4R+TaqBiJsggUTpZmGpH1+dqdC+U_s1w@mail.gmail.com>
         <e7e49ed5-09e2-da48-002d-c7eccc9f9451@intel.com>
         <CAA85sZtyM+X_oHcpOBNSgF=kmB6k32bpB8FCJN5cVE14YCba+A@mail.gmail.com>
         <22aad588-47d6-6441-45b2-0e685ed84c8d@intel.com>
         <CAA85sZti1=ET=Tc3MoqCX0FqthHLf6MSxGNAhJUNiMms1TfoKA@mail.gmail.com>
         <CAA85sZvn04k7=oiTQ=4_C8x7pNEXRWzeEStcaXvi3v63ah7OUQ@mail.gmail.com>
         <ffb554bfa4739381d928406ad24697a4dbbbe4a2.camel@redhat.com>
         <CAA85sZunA=tf0FgLH=MNVYq3Edewb1j58oBAoXE1Tyuy3GJObg@mail.gmail.com>
         <CAA85sZsH1tMwLtL=VDa5=GBdVNWgifvhK+eG-hQg69PeSxBWkg@mail.gmail.com>
         <CAA85sZu=CzJx9QD87-vehOStzO9qHUSWk6DXZg3TzJeqOV5-aw@mail.gmail.com>
         <0a040331995c072c56fce58794848f5e9853c44f.camel@redhat.com>
         <CAA85sZuuwxtAQcMe3LHpFVeF7y-bVoHtO1nukAa2+NyJw3zcyg@mail.gmail.com>
         <CAA85sZurk7-_0XGmoCEM93vu3vbqRgPTH4QVymPR5BeeFw6iFg@mail.gmail.com>
         <486ae2687cd2e2624c0db1ea1f3d6ca36db15411.camel@redhat.com>
         <CAA85sZsJEZK0g0fGfH+toiHm_o4pdN+Wo0Wq9fgsUjHXGxgxQA@mail.gmail.com>
         <CAA85sZs4KkfVojx=vxbDaWhWRpxiHc-RCc2OLD2c+VefRjpTfw@mail.gmail.com>
         <5688456234f5d15ea9ca0f000350c28610ed2639.camel@redhat.com>
         <CAA85sZvT-vAHQooy8+i0-bTxgv4JjkqMorLL1HjkXK6XDKX41w@mail.gmail.com>
         <CAA85sZs2biYueZsbDqdrMyYfaqH6hnSMpymgbsk=b3W1B7TNRA@mail.gmail.com>
         <CAA85sZs_H3Dc-mYnj8J5VBEwUJwbHUupP+U-4eG20nfAHBtv4w@mail.gmail.com>
         <92a4d42491a2c219192ae86fa04b579ea3676d8c.camel@redhat.com>
         <CAA85sZvtspqfep+6rH8re98-A6rHNNWECvwqVaM=r=0NSSsGzA@mail.gmail.com>
         <dfbbe91a9c0abe8aba2c00afd3b7f7d6af801d8e.camel@redhat.com>
         <CAA85sZuQh0FMoGDFVyOad6G1UB9keodd3OCZ4d4r+xgXDArcVA@mail.gmail.com>
         <062061fc4d4d3476e3b0255803b726956686eb19.camel@redhat.com>
         <CAA85sZv9KCmw8mAzK4T-ORXB48wuLF+YXTYSWxkBhv3k_-wzcA@mail.gmail.com>
         <CAA85sZt6ssXRaZyq4awM0yTLFk62Gxbgw-0+bTKWsHwQvVzZXQ@mail.gmail.com>
         <d9bf21296a4691ac5aca11ccd832765b262f7088.camel@redhat.com>
         <CAA85sZsidN4ig=RaQ34PYFjnZGU-=zqR=r-5za=G4oeAtxDA7g@mail.gmail.com>
         <14cd6a50bd5de13825017b75c98cb3115e84acc1.camel@redhat.com>
         <CAA85sZuZLg+L7Sr51PPaOkPKbbiywXbbKzhTyjaw12_S6CsZHQ@mail.gmail.com>
         <c6cf7b4c0a561700d2015c970d52fc9d92b114c7.camel@redhat.com>
         <CAA85sZvZ_X=TqCXaPui0PDLq2pp5dw_uhga+wcXgBqudrLP9bQ@mail.gmail.com>
         <67ff0f7901e66d1c0d418c48c9a071068b32a77d.camel@redhat.com>
         <CANn89i+F=R71refT8K_8hPaP+uWn15GeHz+FTMYU=VPTG24WFA@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.46.4 (3.46.4-1.fc37) 
MIME-Version: 1.0
Precedence: bulk

On Thu, 2023-07-06 at 15:56 +0200, Eric Dumazet wrote:
> On Thu, Jul 6, 2023 at 3:02=E2=80=AFPM Paolo Abeni <pabeni@redhat.com> wr=
ote:
> >=20
> > On Thu, 2023-07-06 at 13:27 +0200, Ian Kumlien wrote:
> > > On Thu, Jul 6, 2023 at 10:42=E2=80=AFAM Paolo Abeni <pabeni@redhat.co=
m> wrote:
> > > > On Wed, 2023-07-05 at 15:58 +0200, Ian Kumlien wrote:
> > > > > On Wed, Jul 5, 2023 at 3:29=E2=80=AFPM Paolo Abeni <pabeni@redhat=
.com> wrote:
> > > > > >=20
> > > > > > On Wed, 2023-07-05 at 13:32 +0200, Ian Kumlien wrote:
> > > > > > > On Wed, Jul 5, 2023 at 12:28=E2=80=AFPM Paolo Abeni <pabeni@r=
edhat.com> wrote:
> > > > > > > >=20
> > > > > > > > On Tue, 2023-07-04 at 16:27 +0200, Ian Kumlien wrote:
> > > > > > > > > More stacktraces.. =3D)
> > > > > > > > >=20
> > > > > > > > > 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)
> > > > > > > >=20
> > > > > > > > I'm really running out of ideas here...
> > > > > > > >=20
> > > > > > > > This is:
> > > > > > > >=20
> > > > > > > >         WARN_ON_ONCE(UDP_SKB_CB(skb)->partial_cov);
> > > > > > > >=20
> > > > > > > > sort of hint skb being shared (skb->users > 1) while enqueu=
ed 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.
> > > > > > > >=20
> > > > > > > > Anyway the other splats reported here and in later emails a=
re
> > > > > > > > compatible with shared skbs.
> > > > > > > >=20
> > > > > > > > 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).
> > > > > > >=20
> > > > > > > With rx-gro-list off, as in never turned on, everything seems=
 to run fine
> > > > > > >=20
> > > > > > > > * do you have by chance qdiscs on top of the VM tun devices=
?
> > > > > > >=20
> > > > > > > default qdisc is fq
> > > > > >=20
> > > > > > IIRC libvirt could reset the qdisc to noqueue for the owned tun
> > > > > > devices.
> > > > > >=20
> > > > > > Could you please report the output of:
> > > > > >=20
> > > > > > tc -d -s qdisc show dev <tun dev name>
> > > > >=20
> > > > > I don't have these set:
> > > > > CONFIG_NET_SCH_INGRESS
> > > > > CONFIG_NET_SCHED
> > > > >=20
> > > > > so tc just gives an error...
> > > >=20
> > > > The above is confusing. AS CONFIG_NET_SCH_DEFAULT depends on
> > > > CONFIG_NET_SCHED, you should not have a default qdisc, too ;)
> > >=20
> > > Well it's still set in sysctl - dunno if it fails
> > >=20
> > > > Could you please share your kernel config?
> > >=20
> > > Sure...
> > >=20
> > > As a side note, it hasn't crashed - no traces since we did the last c=
hange
> >=20
> > It sounds like an encouraging sing! (last famous words...). I'll wait 1
> > more day, than I'll submit formally...
> >=20
> > > For reference, this is git diff on the running kernels source tree:
> > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > > index cea28d30abb5..1b2394ebaf33 100644
> > > --- a/net/core/skbuff.c
> > > +++ b/net/core/skbuff.c
> > > @@ -4270,6 +4270,17 @@ struct sk_buff *skb_segment_list(struct sk_buf=
f *skb,
> > >=20
> > >         skb_push(skb, -skb_network_offset(skb) + offset);
> > >=20
> > > +       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_header_unclone(skb, GFP_ATOMIC);
> > > +       if (err)
> > > +               goto err_linearize;
> > > +
> > >         skb_shinfo(skb)->frag_list =3D NULL;
> > >=20
> > >         while (list_skb) {
> >=20
> > ...the above check only, as the other 2 should only catch-up side
> > effects of lack of this one. In any case the above address a real
> > issue, so we likely want it no-matter-what.
> >=20
>=20
> Interesting, I wonder if this could also fix some syzbot reports
> Willem and I are investigating.
>=20
> Any idea of when the bug was 'added' or 'revealed' ?

The issue specifically addressed above should be present since
frag_list introduction commit 3a1296a38d0c ("net: Support GRO/GSO
fraglist chaining."). AFAICS triggering it requires non trivial setup -
mcast rx on bridge with frag-list enabled and forwarding to multiple
ports - so perhaps syzkaller found it later due to improvements on its
side ?!?

Cheers,

Paolo