netdev - Re: [PATCH net-next 1/2] net/sched: act

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Message-ID: <CAM0EoMmoMUtrBHyYUWNeBnFFj8kDFYPyQB+O1fdGB4xk_bMWZA@mail.gmail.com>
Date: Wed, 26 Nov 2025 15:20:15 -0500
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net, pabeni@...hat.com, 
	jiri@...nulli.us, xiyou.wangcong@...il.com, netdev@...r.kernel.org, 
	dcaratti@...hat.com
Subject: Re: [PATCH net-next 1/2] net/sched: act_mirred: Fix infinite loop

On Wed, Nov 26, 2025 at 1:20 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Wed, Nov 26, 2025 at 10:14 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> > It's the multiport redirection, particularly to ingress. When it get
> > redirected to ingress it will get queued and then transitioned back.
> > xmit struct wont catch this as a recursion, so MIRRED_NEST_LIMIT will
> > not help you.
> > Example (see the first accompanying tdc test):
> > packet showing up on port0:ingress mirred redirect --> port1:egress
> > packet showing up on port1:egress mirred redirect --> port0:ingress
>
> Have you tried recording both devices ?
>
> diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
> index f27b583def78e4afecc7112854b93d59c2520201..711fc2e31cb0451c07a39f9c94226357d5faec09
> 100644
> --- a/net/sched/act_mirred.c
> +++ b/net/sched/act_mirred.c
> @@ -445,15 +445,17 @@ TC_INDIRECT_SCOPE int tcf_mirred_act(struct sk_buff *skb,
>                 return retval;
>         }
>         for (i = 0; i < xmit->sched_mirred_nest; i++) {
> -               if (xmit->sched_mirred_dev[i] != dev)
> +               if (xmit->sched_mirred_dev[i] != dev &&
> +                   xmit->sched_mirred_dev[i] != skb->dev)
>                         continue;
> -               pr_notice_once("tc mirred: loop on device %s\n",
> -                              netdev_name(dev));
> +               pr_notice_once("tc mirred: loop on device %s/%s\n",
> +                              netdev_name(dev), netdev_name(skb->dev));
>                 tcf_action_inc_overlimit_qstats(&m->common);
>                 return retval;
>         }
>
>         xmit->sched_mirred_dev[xmit->sched_mirred_nest++] = dev;
> +       xmit->sched_mirred_dev[xmit->sched_mirred_nest++] = skb->dev;
>
>         m_mac_header_xmit = READ_ONCE(m->tcfm_mac_header_xmit);
>         m_eaction = READ_ONCE(m->tcfm_eaction);

Did you mean not to decrement sched_mirred_nest twice?
I dont have time today but will continue early AM.

cheers,
jamal