linux-kernel - Re: system gets stuck in a lock during boot

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Date:	Mon, 24 Aug 2009 00:54:08 -0700
From:	"Justin P. Mattock" <justinmattock@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Li Zefan <lizf@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: system gets stuck in a lock during boot

Peter Zijlstra wrote:
> On Mon, 2009-08-24 at 14:13 +0800, Li Zefan wrote:
>    
>> Peter Zijlstra wrote:
>>      
>>> On Mon, 2009-08-24 at 10:41 +0800, Li Zefan wrote:
>>>
>>>        
>>>>> @@ -940,7 +940,7 @@ event_create_dir(struct ftrace_event_call *call, struct dentr
>>>>>                  entry = trace_create_file("enable", 0644, call->dir, call,
>>>>>                                            enable);
>>>>>
>>>>> -       if (call->id)
>>>>> +       if (call->id&&  call->profile_enable)
>>>>>            
>>>> We do an extra check on ->profile_enable, shouldn't cause bug..
>>>>
>>>>          
>>>>>                  entry = trace_create_file("id", 0444, call->dir, call,
>>>>>                                            id);
>>>>>            
>>>> Any way, I don't think this commit does the right thing:
>>>>
>>>>    - If CONFIG_EVENT_PROFILE=y, we'll create events/<dir>/<event>/id,
>>>>      except events/ftrace/<event>/id.
>>>>
>>>>    - if CONFIG_EVENT_PROFILE=n, there's no 'id' file at all!
>>>>
>>>> I think it's better to skip ftrace/ dir in perf tool code, instead of
>>>> skipping creating id files in ftrace code.
>>>>          
>>> No, it does do the right thing. Your patch breaks things because not all
>>> tracepoints are created through TRACE_EVENT() and will thus not have
>>> their profile_enable/disable hooks set.
>>>
>>> By giving them an ID file, there is no way to distinguish good from bad
>>> tracepoints.
>>>
>>>        
>> But removing the id file from events/ftrace/ might break some ftrace
>> binary parsers?
>>
>> And this commit makes 'id' file disapeared with CONFIG_EVENT_PROFILE=n.
>>      
>
> I introduced the id file for EVENT_PROFILE, tough luck if someone else
> relies on it.
>
>    
>>> Expempting ftrace is no solid solution, suppose someone else does a
>>> TRACE_EVENT_FORMAT() tracepoint, how would you know you could use it as
>>> a profile event source?
>>>
>>>        
>> Agree.
>>
>>      
>>> The id files really must stay conditional.
>>>
>>>        
>> I don't think it's a good idea to connect it with perfcounter
>> this way. Wouldn't adding a 'profilable' file more intuitive?
>>      
>
> its called: id ;-)
>
>    
Alright, I'm going to go back to the beginning
and start my build from scratch(make sure things are legit).

Justin P. Mattock

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