linux-kernel - Re: [PATCH] tracing, sched: mark preempt

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Message-ID: <4A8B6C80.4050805@cn.fujitsu.com>
Date:	Wed, 19 Aug 2009 11:07:44 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing, sched: mark preempt_schedule() notrace

Steven Rostedt wrote:
> 
> On Tue, 18 Aug 2009, Frederic Weisbecker wrote:
> 
>> On Tue, Aug 18, 2009 at 04:01:57PM +0800, Lai Jiangshan wrote:
>>> Current preempt_schedule() is not marked notrace. It may be
>>> infinite recursion in __trace_graph_return().
>>>
>>> preempt_schedule()
>>>   __trace_graph_return()
>>>     ftrace_preempt_disable() (!!return false!!)
>>>     ftrace_preempt_enable()
>>>       preempt_enable_notrace()
>>>          preempt_schedule() (need_resched() may be true again)
>>
>>
>> It would happen in __trace_graph_return() , when preempt_schedule()
>> has finished its job. It's very unlikely the TIF_NEED_RESCHED is
>> set just after (because it has just been cleared).
>> But why not. In that case, preempt_schedule() is called again but it's
>> not a real tracing recursion.
>>
>> That seems like a normal behaviour actually.
> 
> In fact, this is actually something to be traced. I would not add a 
> notrace to it. This is not saving anything, the trace_graph_return does 
> not need to worry about stack overflow, since the return code already 
> freed the stack.
> 

You're right, I forgot to read trace_graph_return().
trace_graph_return() protects itself from recursion.

Since there is no may-recursive trace_func_graph_ret_t.
Just omit this patch.
Sorry for bothered you all.


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