linux-kernel - Re: timer: lockup in run_timer

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Message-ID: <1373561972.17876.51.camel@gandalf.local.home>
Date:	Thu, 11 Jul 2013 12:59:32 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Dave Jones <davej@...hat.com>, Tejun Heo <tj@...nel.org>,
	tglx@...utronix.de, LKML <linux-kernel@...r.kernel.org>,
	trinity@...r.kernel.org
Subject: Re: timer: lockup in run_timer_softirq()

On Thu, 2013-07-11 at 12:55 -0400, Steven Rostedt wrote:

> > 
> > Other than that, a function tracer environment that is safer to use might be
> > useful for other people as well.
> 
> Not sure how to make the environment safe, as the main purpose of the
> function trace is to debug those hard to debug locations, like NMIs,
> RCU, dynamic ticks, etc. To ensure a "safe" environment, it would
> cripple the tracer.
> 
> Hmm, what would you state as a safe environment? How can we detect if
> the environment is safe to trace or not?

Maybe I misunderstood you. You mean to have this environment be
something for not just perf, and have the macro be:

NONSAFE_TRACE(__local_bh_enable);

?

Then, any ftrace user could set a flag in the registering of its ops to
'safe_only_functions'. And it will ignore all of these locations.
There's really not many of them, so it may not be too hard to weed out.

-- Steve


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