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Subject: Re: [PATCH 1/2] tracing: Add sysctl to enable/disable tracing on
 oops
From: Steven Rostedt <rostedt@goodmis.org>
Reply-To: rostedt@goodmis.org
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>, Frederic Weisbecker <fweisbec@gmail.com>,
       LKML <linux-kernel@vger.kernel.org>
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Date: Tue, 08 Sep 2009 22:04:27 -0400
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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.

-- Steve