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

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Message-Id: <1251096925.7538.121.camel@twins>
Date:	Mon, 24 Aug 2009 08:55:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Li Zefan <lizf@...fujitsu.com>
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

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 ;-)
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