netdev - Re: [PATCH net-next v3 3/3] tcp: add location into reset trace process

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Message-ID: <CAL+tcoD0_tPkmp-jDg8tiQhcwoR6Lb_BwqiZ4xegoxObxsy86g@mail.gmail.com>
Date: Fri, 29 Mar 2024 18:40:54 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: mhiramat@...nel.org, mathieu.desnoyers@...icios.com, rostedt@...dmis.org, 
	kuba@...nel.org, pabeni@...hat.com, davem@...emloft.net, 
	netdev@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v3 3/3] tcp: add location into reset trace process

On Fri, Mar 29, 2024 at 5:13 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Fri, Mar 29, 2024 at 4:43 AM Jason Xing <kerneljasonxing@...il.com> wrote:
> >
> > From: Jason Xing <kernelxing@...cent.com>
> >
> > In addition to knowing the 4-tuple of the flow which generates RST,
> > the reason why it does so is very important because we have some
> > cases where the RST should be sent and have no clue which one
> > exactly.
> >
> > Adding location of reset process can help us more, like what
> > trace_kfree_skb does.
>
> Well, I would prefer a drop_reason here, even if there is no 'dropped' packet.

Good idea really. Then we can accurately diagnose which kind of reason
exactly causes the RST behavior.

I'm not sure if we can reuse the drop_reason here, like adding/using
some reasons in enum skb_drop_reason {}? The name is a little bit
strange.

Oh, I can just print the string of reason directly instead of really
using enum skb_drop_reason {}...

>
> This would be more stable than something based on function names that
> could be changed.
>
> tracepoints do not have to get ugly, we can easily get stack traces if needed.
>
> perf record -a -g  -e tcp:tcp_send_reset ...

Ah, yes, I blindly mimic what trace_skb_kfree() and
trace_consume_skb() do. Introducing some RST reasons is more
reasonable and easier to detect since it's not hard to add four or
five reasons only.

Thanks,
Jason