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

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Date:	Mon, 24 Aug 2009 07:58:43 +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 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.

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?

The id files really must stay conditional.

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.
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