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

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Date:	Mon, 24 Aug 2009 14:13:22 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"Justin P. Mattock" <justinmattock@...il.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 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.

> 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?

> Aside from that, you only add #ifdef fuzz back which with his config is
> moot, and shouldn't result in anything but a slightly bigger structure
> to begin with.
> 

Yeah, actually I still fail to see where the bug is, maybe
the commit that Justin bisected down is not the real culprit..

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