netdev - Re: [Intel-wired-lan] bug with rx-udp-gro-forwarding offloading?

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Date: Wed, 05 Jul 2023 15:29:04 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Ian Kumlien <ian.kumlien@...il.com>
Cc: Alexander Lobakin <aleksander.lobakin@...el.com>, intel-wired-lan
 <intel-wired-lan@...ts.osuosl.org>, Jakub Kicinski <kuba@...nel.org>, Eric
 Dumazet <edumazet@...gle.com>, "netdev@...r.kernel.org"
 <netdev@...r.kernel.org>,  "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>
Subject: Re: [Intel-wired-lan] bug with rx-udp-gro-forwarding offloading?

On Wed, 2023-07-05 at 13:32 +0200, Ian Kumlien wrote:
> On Wed, Jul 5, 2023 at 12:28 PM Paolo Abeni <pabeni@...hat.com> wrote:
> > 
> > On Tue, 2023-07-04 at 16:27 +0200, Ian Kumlien wrote:
> > > More stacktraces.. =)
> > > 
> > > 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

IIRC libvirt could reset the qdisc to noqueue for the owned tun
devices.

Could you please report the output of:

tc -d -s qdisc show dev <tun dev name>

Thanks!

/P