netdev - Re: [PATCH net 5/6] net/sched: fix packet loop on netem when duplicate is on

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Message-ID: <CAM_iQpUEgzQwrO5DJ05Rzx8CJJ660xZPcGqoD_SPJ2buo7K_Cg@mail.gmail.com>
Date: Tue, 13 Jan 2026 11:32:12 -0800
From: Cong Wang <xiyou.wangcong@...il.com>
To: Jamal Hadi Salim <jhs@...atatu.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, horms@...nel.org, andrew+netdev@...n.ch, 
	netdev@...r.kernel.org, jiri@...nulli.us, victor@...atatu.com, 
	dcaratti@...hat.com, lariel@...dia.com, daniel@...earbox.net, 
	pablo@...filter.org, kadlec@...filter.org, fw@...len.de, phil@....cc, 
	netfilter-devel@...r.kernel.org, coreteam@...filter.org, 
	zyc199902@...omail.cn, lrGerlinde@...lfence.com, jschung2@...ton.me, 
	William Liu <will@...lsroot.io>, Savino Dicanosa <savy@...t3mfailure.io>
Subject: Re: [PATCH net 5/6] net/sched: fix packet loop on netem when
 duplicate is on

On Sun, Jan 11, 2026 at 1:57 PM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> On Sun, Jan 11, 2026 at 3:39 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > On Sun, Jan 11, 2026 at 8:40 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
> > > -               q->duplicate = 0;
> > > +               skb2->ttl++; /* prevent duplicating a dup... */
> > >                 rootq->enqueue(skb2, rootq, to_free);
> > > -               q->duplicate = dupsave;
> >
> > As I already explained many times, the ROOT cause is enqueuing
> > to the root qdisc, not anything else.
> >
> > We need to completely forget all the kernel knowledge and ask
> > a very simple question here: is enqueuing to root qdisc a reasonable
> > use? More importantly, could we really define it?
> >
> > I already provided my answer in my patch description, sorry for not
> > keeping repeating it for at least the 3rd time.
> >
> > Therefore, I still don't think you fix the root cause here. The
> > problematic behavior of enqueuing to root qdisc should be corrected,
> > regardless of any kernel detail.
> >
>
> The root cause is a loop in the existing code, present since the

That's the symptom, not the cause.