netdev - Re: [PATCH net 1/2] net: sched: drop ct for the packets toward ingress only in act

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Date:   Wed, 22 Sep 2021 13:17:05 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     network dev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Davide Caratti <dcaratti@...hat.com>,
        Hangbin Liu <liuhangbin@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH net 1/2] net: sched: drop ct for the packets toward
 ingress only in act_mirred

On Wed, Sep 22, 2021 at 11:43 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> On Tue, Sep 21, 2021 at 12:02 AM Xin Long <lucien.xin@...il.com> wrote:
> >
> > On Tue, Sep 21, 2021 at 2:31 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
> > >
> > > On Mon, Sep 20, 2021 at 7:12 AM Xin Long <lucien.xin@...il.com> wrote:
> > > >
> > > > nf_reset_ct() called in tcf_mirred_act() is supposed to drop ct for
> > > > those packets that are mirred or redirected to only ingress, not
> > > > ingress and egress.
> > >
> > > Any reason behind this? I think we at least need to reset it when
> > > redirecting from ingress to egress as well? That is, when changing
> > > directions?
> > For the reason why ct should be reset, it's said in
> > d09c548dbf3b ("net: sched: act_mirred: Reset ct info when mirror").
> > The user case is OVS HWOL using TC to do NAT and then redirecting
> > the NATed skb back to the ingress of one local dev, it's ingress only, this
> > patch is more like to minimize the side effect of d09c548dbf3b IF there is.
>
> What is the side effect here? Or what is wrong with resetting CT on
> egress side?
>
> >
> > Not sure if it's too much to do for that from ingress to egress.
> > What I was thinking is this should happen on rx path(ingress), like it
> > does in internal_dev_recv() in the OVS kernel module. But IF there is
> > any user case needing doing this for ingress to egress, I would add it.
>
> If that is the case, then this patch is completely unnecessary. So
> instead of going back and forth, please elaborate on why resetting
> CT for egress is a problem here.
What I'm afraid is: after resetting CT for the packets redirected to egress,
the tc rules on the next dev egress that may need these CT will break.

I can't give a use case right now, and just don't want to introduce extra
change for which we don't see a use. If you think that's safe, I'm fine
to do these resets when the direction is changed.