netdev - Re: [Patch v2 net 1/2] netem: Fix skb duplication logic to prevent infinite loops

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Message-ID: <CAM0EoMmToF2ihqsSGEDyG3NAcy4rjO5pzXjShD2ac7VrjDNwvA@mail.gmail.com>
Date: Tue, 8 Jul 2025 09:19:50 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Simon Horman <horms@...nel.org>
Cc: Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org, will@...lsroot.io, 
	stephen@...workplumber.org, Savino Dicanosa <savy@...t3mfailure.io>
Subject: Re: [Patch v2 net 1/2] netem: Fix skb duplication logic to prevent
 infinite loops

On Tue, Jul 8, 2025 at 9:18 AM Simon Horman <horms@...nel.org> wrote:
>
> On Mon, Jul 07, 2025 at 12:50:14PM -0700, Cong Wang wrote:
> > This patch refines the packet duplication handling in netem_enqueue() to ensure
> > that only newly cloned skbs are marked as duplicates. This prevents scenarios
> > where nested netem qdiscs with 100% duplication could cause infinite loops of
> > skb duplication.
> >
> > By ensuring the duplicate flag is properly managed, this patch maintains skb
> > integrity and avoids excessive packet duplication in complex qdisc setups.
> >
> > Now we could also get rid of the ugly temporary overwrite of
> > q->duplicate.
> >
> > Fixes: 0afb51e72855 ("[PKT_SCHED]: netem: reinsert for duplication")
> > Reported-by: William Liu <will@...lsroot.io>
> > Reported-by: Savino Dicanosa <savy@...t3mfailure.io>
> > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
>
> Reviewed-by: Simon Horman <horms@...nel.org>

Simon,
This patch wont work - see the sample config i presented.

cheers,
jamal