netdev - Re: question: ip forwarding and fq/mq qdisc

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Date:   Fri, 14 Dec 2018 17:12:44 +0300
From:   Sergey Matyukevich <geomatsi@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        sergey.matyukevich.os@...ntenna.com
Subject: Re: question: ip forwarding and fq/mq qdisc

> > Hi all,
> > 
> > I have been running 4.18-rc8 kernel with enabled IP forwarding between
> > wired and wireless interfaces, where both interfaces
> > were configured as fq qdisc.
> > 
> > However after moving to 4.20-rc1 kernel the same configuration does not
> > work anymore: pass-through packets are not forwarded in both directions.
> > Forwarding starts working again only if I change qdisc of _both_ interfaces
> > to anything but fq/mq. For instance any combination of pfifo/fq_codel/noqueue
> > works fine.
> > 
> > Does it look like a regression or it is a known change in behavior ?
> > 
> > Regards,
> > Sergey
> > 
> 
> Hi Sergey
> 
> I guess EDT model broke this use case.
> 
> I was under the impression skb->tstamp was cleared when forwarding packets, maybe I was wrong.
> 
> Can you try the following ?
> 
> diff --git a/net/ipv4/ip_forward.c b/net/ipv4/ip_forward.c
> index 06ee4696703c0ce72ea914403b739839e60f1584..00ec819f949b5e76ea96be901a697f4e12d5cf4d 100644
> --- a/net/ipv4/ip_forward.c
> +++ b/net/ipv4/ip_forward.c
> @@ -79,6 +79,7 @@ static int ip_forward_finish(struct net *net, struct sock *sk, struct sk_buff *s
>         if (unlikely(opt->optlen))
>                 ip_forward_options(skb);
>  
> +       skb->tstamp = 0;
>         return dst_output(net, sk, skb);
>  }

Hi Eric,

This patch fixes the issue: ip forwarding works for fq/mq qdisc.

Thanks,
Sergey