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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: rostedt@goodmis.org
Subject: Re: [PATCH 1/2] tracing: Add sysctl to enable/disable tracing on oops
Cc: kosaki.motohiro@jp.fujitsu.com, Li Zefan <lizf@cn.fujitsu.com>,
       Ingo Molnar <mingo@elte.hu>, Frederic Weisbecker <fweisbec@gmail.com>,
       LKML <linux-kernel@vger.kernel.org>
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Date: Wed,  9 Sep 2009 11:33:46 +0900 (JST)
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> On Wed, 2009-09-09 at 09:47 +0800, Li Zefan wrote:
> > Steven Rostedt wrote:
> > > On Wed, 2009-09-09 at 09:37 +0800, Li Zefan wrote:
> > >> Steven Rostedt wrote:
> > >>> On Wed, 2009-09-09 at 09:15 +0800, Li Zefan wrote:
> > >>>> Currently we always disable tracing on oops, and this patch
> > >>>> adds a sysctl so one can choose to enable it.
> > >>> Hmm, we already have a way to enable it.
> > >>>
> > >>> # echo 1 > /debug/tracing/tracing_on
> > >>>
> > >> What I want is a way to not disable it when an oops happened. :)
> > >>
> > > 
> > > Ah, I misunderstood. May I ask a silly question?
> > > 
> > > Why?
> > > 
> > 
> > Otherwise we won't get trace output from trae_crash_kexec if
> > crash_kexec() is not called by panic(). For example:
> > 
> >   oops_begin()
> > ->trace_off()
> > ->panic_on_oops
> > ->kexec_should_crash()
> > ->crash_kexec()
> 
> OK, but I'm not exactly sure what you final goal is here. To have a
> something to search for in the ring buffer after the crash? Maybe
> instead we can add a "trace_oops" event? Just put it before the
> tracing_off call.

I have another silly question.
Why should we call tracing_off() in oops_enter()?

1. Oops behavior depend on panic_on_oops sysctl.
   Should we disable trace both case?
2. Can I think the code treat to save oops in tracing code?
   or it have more deeper intention?


Can anyone please explain it?