linux-kernel - Re: timer: lockup in run_timer

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Message-ID: <533DC7F5.9090202@oracle.com>
Date:	Thu, 03 Apr 2014 16:43:33 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.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 07/11/2013 01:11 PM, Peter Zijlstra wrote:
> On Thu, Jul 11, 2013 at 12:59:32PM -0400, Steven Rostedt wrote:
>> 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.
> 
> Yah, like that. But that doesn't invalidate your question as to what 'safe'
> would encompass. I think RCU/lockdep would be the big thing for perf, not
> sure it should be wider than that.

Ping? There was no conclusion here and this issue is still ongoing in -next.


Thanks,
Sasha

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