netdev - Re: [PATCH net] net/sched: properly init chain in case of multiple control actions

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Date:   Mon, 15 Oct 2018 11:31:01 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Davide Caratti <dcaratti@...hat.com>
Cc:     Jiri Pirko <jiri@...nulli.us>, Jamal Hadi Salim <jhs@...atatu.com>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net/sched: properly init chain in case of multiple
 control actions

On Sat, Oct 13, 2018 at 8:23 AM Davide Caratti <dcaratti@...hat.com> wrote:
>
> On Fri, 2018-10-12 at 13:57 -0700, Cong Wang wrote:
> > Why not just validate the fallback action in each action init()?
> > For example, checking tcfg_paction in tcf_gact_init().
> >
> > I don't see the need of making it generic.
>
> hello Cong, once again thanks for looking at this.
>
> what you say is doable, and I evaluated doing it before proposing this
> patch.
>
> But I felt unconfortable, because I needed to pass struct tcf_proto *tp in
> tcf_gact_init() to initialize a->goto_chain with the chain_idx encoded in
> the fallback action. So, I would have changed all the init() functions in
> all TC actions, just to fix two of them.
>
> A (legal?) trick  is to let tcf_action store the fallback action when it
> contains a 'goto chain' command, I just posted a proposal for gact. If you
> think it's ok, I will test and post the same for act_police.

Do we really need to support TC_ACT_GOTO_CHAIN for
gact->tcfg_paction etc.? I mean, is it useful in practice or is it just for
completeness?

IF we don't need to support it, we can just make it invalid without needing
to initialize it in ->init() at all.

If we do, however, we really need to move it into each ->init(), because
we have to lock each action if we are modifying an existing one. With
your patch, tcf_action_goto_chain_init() is still called without the per-action
lock.

What's more, if we support two different actions in gact, that is, tcfg_paction
and tcf_action, how could you still only have one a->goto_chain pointer?
There should be two pointers for each of them. :)

Thanks.