netdev - Re: [PATCH net-next v6 0/7] Implement reset reason mechanism to detect

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Message-ID: <CAL+tcoBVYWaMAYRdBC6UKiNuhdR7cK+570=0Kw1MKEhPhBL_AA@mail.gmail.com>
Date: Fri, 19 Apr 2024 06:29:20 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>, dsahern@...nel.org, matttbe@...nel.org, 
	martineau@...nel.org, geliang@...nel.org, pabeni@...hat.com, 
	davem@...emloft.net, rostedt@...dmis.org, mhiramat@...nel.org, 
	mathieu.desnoyers@...icios.com, atenart@...nel.org, mptcp@...ts.linux.dev, 
	netdev@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v6 0/7] Implement reset reason mechanism to detect

On Fri, Apr 19, 2024 at 2:51 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Thu, Apr 18, 2024 at 6:24 PM Jason Xing <kerneljasonxing@...il.com> wrote:
> >
> > On Thu, Apr 18, 2024 at 11:46 PM Jakub Kicinski <kuba@...nel.org> wrote:
> > >
> > > On Thu, 18 Apr 2024 11:30:02 +0800 Jason Xing wrote:
> > > > I'm not sure why the patch series has been changed to 'Changes
> > > > Requested', until now I don't think I need to change something.
> > > >
> > > > Should I repost this series (keeping the v6 tag) and then wait for
> > > > more comments?
> > >
> > > If Eric doesn't like it - it's not getting merged.
> >
> > I'm not a English native speaker. If I understand correctly, it seems
> > that Eric doesn't object to the patch series. Here is the quotation
> > [1]:
> > "If you feel the need to put them in a special group, this is fine by me."
> >
> > This rst reason mechanism can cover all the possible reasons for both
> > TCP and MPTCP. We don't need to reinvent some definitions of reset
> > reasons which are totally the same as drop reasons. Also, we don't
> > need to reinvent something to cover MPTCP. If people are willing to
> > contribute more rst reasons, they can find a good place.
> >
> > Reset is one big complicated 'issue' in production. I spent a lot of
> > time handling all kinds of reset reasons daily. I'm apparently not the
> > only one. I just want to make admins' lives easier, including me. This
> > special/separate reason group is important because we can extend it in
> > the future, which will not get confused.
> >
> > I hope it can have a chance to get merged :) Thank you.
> >
> > [1]: https://lore.kernel.org/all/CANn89i+aLO_aGYC8dr8dkFyi+6wpzCGrogysvgR8FrfRvaa-Vg@mail.gmail.com/
> >
> > Thanks,
> > Jason
>
> My objection was these casts between enums. Especially if hiding with (u32)

So I should explicitly cast it like this:
    tcp_v4_send_reset(rsk, skb, (enum sk_rst_reason)reason);
?

>
> I see no reason for adding these casts in TCP stack.

Sorry, I don't know why the casts really make you so annoyed. But I
still think it's not a bad way to handle all the cases for RST.

Supposing not to add a enum sk_rst_reason{}, passing drop reasons only
works well in TCP for passive rests. For active reset cases (in the
tcp_send_active_reset()), it's meaningless/confusing to insist on
reusing the drop reason because I have to add some reset reasons (that
are only used in RST cases) in the enum skb_drop_reason{}, which is
really weird, in my view. The same problem exists in how to handle
MPTCP. So I prefer putting them in a separate group like now. What do
you think about it, right now?

Thanks,
Jason