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Date: Wed, 9 Sep 2009 13:19:29 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To: rostedt@...dmis.org
Cc: kosaki.motohiro@...fujitsu.com, Li Zefan <lizf@...fujitsu.com>,
Ingo Molnar <mingo@...e.hu>,
Frederic Weisbecker <fweisbec@...il.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] tracing: Add sysctl to enable/disable tracing on oops
> On Wed, 2009-09-09 at 10:40 +0800, Li Zefan wrote:
>
> > > I have another silly question.
> > > Why should we call tracing_off() in oops_enter()?
> > >
> >
> > I guess it's because trace outputs generated during oops can
> > overwrite/mess up those generated before oops?
> >
> > It was added by this commit, but I can't find trace_printk_on_oops.
>
> That's because Thomas did not bother looking up the actual variable he
> was talking about. s/trace_printk_on_oops/ftrace_dump_on_oops/
After a bit thinking, I think ftrace_dump_on_oops and kernel dump with panic have
very similar requirement.
Then, I think we can reuse this infrastructure for kernel dump.
Requirement
- Need to know why the problem occur.
- Need to don't logging oops (panic) internal.
Unfortunately, panic() call panic_notifier after crash_kexec().
it mean tracing_off() was not called when panic on the machine w/ kernel-dump.
NORET_TYPE void panic(const char * fmt, ...)
{
(snip)
crash_kexec(NULL);
(snip)
atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
I think we can insert tracing_off() into panic() directly. it only
bit mask operation, it mean it don't have side effect risk.
Perhaps, There are other kernel dump specific requrement. but I guess
it's very small. Maybe it can be handled by trace_die_handler() or something like.
What do you think?
>
> -- Steve
>
> >
> > commit bdff78707f3ce47e891f3201c9666122a70556ce
> > Author: Thomas Gleixner <tglx@...utronix.de>
> > Date: Fri Jul 24 15:30:45 2009 -0400
> >
> > trace: stop tracer in oops_enter()
> >
> > If trace_printk_on_oops is set we lose interesting trace information
> > when the tracer is enabled across oops handling and printing. We want
> > the trace which might give us information _WHY_ we oopsed.
> >
>
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