Re: 4.4.1 skb_warn_bad_offload+0xc5/0x110

[Hannes Frederic Sowa]

On 24.02.2016 02:46, Wakko Warner wrote:
> Please keep me in CC.
>
> Wakko Warner wrote:
> > Hannes Frederic Sowa wrote:
> > > [full-quote for netdev]
> > >
> > > Hello,
> > >
> > > On 16.02.2016 01:08, Wakko Warner wrote:
> > > > I've been seeing the following on some of my VMs ran under qemu.  The VMs do
> > > > not have internet connectivity.  This happened when some files were accessed
> > > > via NFS to another VM (NOTE: Both VMs throw these warnings.  Both VMs are
> > > > running the exact same kernel).  The host is also throwing these warnings
> > > > and is also 4.4.1, but not the same kernel build.
> > > >
> > > > The issue appears to have gone away if I issue the following on the guests
> > > > and on the host (except br0 instead of eth0 on host)
> > > > ethtool -K eth0 gso off gro off ufo off tso off
> > > >
> > > > On the host, br0 does not have any interfaces enslaved except for the
> > > > interface for the VMs and also does not have an IPv4 address assigned.
> >
> > > Can you try the following patch?
> > >
> > > --- a/net/ipv4/ip_output.c
> > > +++ b/net/ipv4/ip_output.c
> > > @@ -1233,6 +1233,9 @@ ssize_t   ip_append_page(struct sock *sk,
> > > struct flowi4 *fl4, struct page *page,
> > >          if (!skb)
> > >                  return -EINVAL;
> > >
> > > +       if (skb->ip_summed != CHECKSUM_PARTIAL)
> > > +               return -EINVAL;
> > > +
> > >          cork->length += size;
> > >          if ((size + skb->len > mtu) &&
> > >              (sk->sk_protocol == IPPROTO_UDP) &&
> >
> > Still received the warning.  I saw it on the host and on one of the VMs.
> > The VM in this case was an nfs server.  The client did not receive the
> > warning.  I should mention that I'm using v3 and udp on the client for the
> > mount options.
> >
> > I'm not sure if this change effected nfsd on one of the VMs, it isn't working
> > at all on it.
>
> I reverted back to the previous kernel for the VM only and the nfsd on the
> one VM started working.
>
> I should note that when I added this change, I only compiled the kernel and
> copied the bzImage file.  I did not recompile any modules nor copy the
> system.map over.

Actually, I could reproduce it locally thus I pushed a slightly 
different patch already. You have to patch all VMs in terms to not get 
the warning in the hypervisor anymore.

Bye,
Hannes