netdev - Re: [Patch net 1/2] netem: Fix skb duplication logic to prevent infinite loops

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Message-ID: <CAM0EoMmDj9TOafynkjVPaBw-9s7UDuS5DoQ_K3kAtioEdJa1-g@mail.gmail.com>
Date: Wed, 2 Jul 2025 10:12:50 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org, will@...lsroot.io, stephen@...workplumber.org, 
	Savino Dicanosa <savy@...t3mfailure.io>
Subject: Re: [Patch net 1/2] netem: Fix skb duplication logic to prevent
 infinite loops

On Tue, Jul 1, 2025 at 9:57 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> On Tue, Jul 01, 2025 at 04:13:05PM -0700, Cong Wang wrote:
> > diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> > index fdd79d3ccd8c..33de9c3e4d1b 100644
> > --- a/net/sched/sch_netem.c
> > +++ b/net/sched/sch_netem.c
> > @@ -460,7 +460,8 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> >       skb->prev = NULL;
> >
> >       /* Random duplication */
> > -     if (q->duplicate && q->duplicate >= get_crandom(&q->dup_cor, &q->prng))
> > +     if (tc_skb_cb(skb)->duplicate &&
>
> Oops, this is clearly should be !duplicate... It was lost during my
> stupid copy-n-paste... Sorry for this mistake.
>

I understood you earlier, Cong. My view still stands:
You are adding logic to a common data structure for a use case that
really makes no sense. The ROI is not good.
BTW: I am almost certain you will hit other issues when this goes out
or when you actually start to test and then you will have to fix more
spots.

cheers,
jamal