netdev - Re: [PATCH RFC net-next v2 1/1] net: sched: Disambiguate verdict from return code

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Date: Mon, 16 Oct 2023 10:11:39 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Davide Caratti <dcaratti@...hat.com>
Cc: Victor Nogueira <victor@...atatu.com>, daniel@...earbox.net, xiyou.wangcong@...il.com, 
	jiri@...nulli.us, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, paulb@...dia.com, bpf@...r.kernel.org, mleitner@...hat.com, 
	martin.lau@...ux.dev, netdev@...r.kernel.org, kernel@...atatu.com
Subject: Re: [PATCH RFC net-next v2 1/1] net: sched: Disambiguate verdict from
 return code

On Mon, Oct 16, 2023 at 10:01 AM Davide Caratti <dcaratti@...hat.com> wrote:
>
> hello Victor, thanks for the patch!
>
> On Sat, Oct 14, 2023 at 03:09:21PM -0300, Victor Nogueira wrote:
> > Currently there is no way to distinguish between an error and a
> > classification verdict. Which has caused us a lot of pain with buggy qdiscs
> > and syzkaller. This patch does 2 things - one is it disambiguates between
> > an error and policy decisions. The reasons are added under the auspices of
> > skb drop reason. We add the drop reason as a part of struct tcf_result.
> > That way, tcf_classify can set a proper drop reason when it fails,
> > and we keep the classification result as the tcf_classify's return value.
> >
> > This patch also adds a variety of drop reasons which are more fine grained
> > on why a packet was dropped by the TC classification action subsystem.
> >
> > Co-developed-by: Daniel Borkmann <daniel@...earbox.net>
> > Signed-off-by: Victor Nogueira <victor@...atatu.com>
> > ---
> >
> > v1 -> v2:
> > - Make tcf_classify set drop reason instead of verdict in struct
> >   tcf_result
> > - Make tcf_classify return verdict (as it was doing before)
> > - Only initialise struct tcf_result in tc_run
> > - Add new drop reasons specific to TC
> > - Merged v1 patch with Daniel's patch (https://lore.kernel.org/bpf/20231013141722.21165ef3@kernel.org/T/)
> >   for completeness
>
> Acked-by: Davide Caratti <dcaratti@...hat.com>
>
> By the way, this might be a chance to remove the "TC mirred to Houston"
> printout and replace it with a proper drop reason (see [1]). WDYT?

sigh. So much history there. I recommend
SKB_DROP_REASON_TC_MIRRED_TO_HOUSTON
/me runs

cheers,
jamal
> thanks,
> --
> davide
>
> [1] https://lore.kernel.org/netdev/Yt2CIl7iCoahCPoU@pop-os.localdomain/
>