Re: DNS (?) not working on G5 (64-bit powerpc) (was [net-next,v3,3/3] udp: try to avoid 2 cache miss on dequeue)

[Paolo Abeni <pabeni@redhat.com>]

On Fri, 2017-06-23 at 16:59 +1000, Michael Ellerman wrote:
> Hannes Frederic Sowa <hannes@stressinduktion.org> writes:
> 
> > On Thu, Jun 22, 2017, at 22:57, Paolo Abeni wrote:
> > > 
> > > Can you please check if the following patch fixes the issue? Only
> > > compiled tested here.
> > > 
> > > Thanks!!!
> > > ---
> > > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > > index 067a607..80d89fe 100644
> > > --- a/net/ipv4/udp.c
> > > +++ b/net/ipv4/udp.c
> > > @@ -1446,16 +1446,19 @@ static struct sk_buff
> > > *__first_packet_length(struct sock *sk,
> > >  {
> > >  	struct sk_buff *skb;
> > >  
> > > -       while ((skb = skb_peek(rcvq)) != NULL &&
> > > -              udp_lib_checksum_complete(skb)) {
> > > -               __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
> > > -                               IS_UDPLITE(sk));
> > > -               __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
> > > -                               IS_UDPLITE(sk));
> > > -               atomic_inc(&sk->sk_drops);
> > > -               __skb_unlink(skb, rcvq);
> > > -               *total += skb->truesize;
> > > -               kfree_skb(skb);
> > > +       while ((skb = skb_peek(rcvq)) != NULL) {
> > > +               if (udp_lib_checksum_complete(skb)) {
> > > +                       __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
> > > +                                       IS_UDPLITE(sk));
> > > +                       __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
> > > +                                       IS_UDPLITE(sk));
> > > +                       atomic_inc(&sk->sk_drops);
> > > +                       __skb_unlink(skb, rcvq);
> > > +                       *total += skb->truesize;
> > > +                       kfree_skb(skb);
> > > +               } else {
> > > +                       udp_set_dev_scratch(skb);
> > 
> > It needs a "break;" here.
> > 
> > > +               }
> > >  	}
> > >  	return skb;
> > >  }
> 
> That works!
> 
> $ wget google.com
> --2017-06-23 16:56:31--  http://google.com/
> Resolving proxy.pmdw.com (proxy.pmdw.com)... 10.1.2.3
> Connecting to proxy.pmdw.com (proxy.pmdw.com)|10.1.2.3|:3128... connected.
> Proxy request sent, awaiting response... 302 Found
> Location: http://www.google.com.au/?gfe_rd=cr&ei=n7tMWeb9JYPr8wfg4LXYAQ [following]
> --2017-06-23 16:56:31--  http://www.google.com.au/?gfe_rd=cr&ei=n7tMWeb9JYPr8wfg4LXYAQ
> Reusing existing connection to proxy.pmdw.com:3128.
> Proxy request sent, awaiting response... 200 OK
> Length: unspecified [text/html]
> Saving to: ‘index.html’
> 
> 
> The patch had whitespace issues or something and I had to apply it by
> hand, here's what I actually tested.

Thank you!

I'll submit formally the patch after some more testing.

I noticed this version has entered the ppc patchwork, but I think that
the formal submission should go towards the net-next tree.

Cheers,

Paolo