linux-kernel - Re: [PATCH] tracing/profile: Fix profile_disable vs module

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Date:	Thu, 27 Aug 2009 18:04:13 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Li Zefan <lizf@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload

On Thu, 2009-08-27 at 11:57 -0400, Steven Rostedt wrote:
> On Thu, 27 Aug 2009, Peter Zijlstra wrote:
> 
> > On Wed, 2009-08-26 at 15:48 -0400, Steven Rostedt wrote:
> > >  									\
> > > @@ -399,16 +413,20 @@ static int ftrace_profile_enable_##call(struct ftrace_event_call *event_call) \
> > >  {									\
> > >  	int ret = 0;							\
> > >  									\
> > > -	if (!atomic_inc_return(&event_call->profile_count))		\
> > > +	if (!atomic_inc_return(&event_call->profile_count)) {		\
> > > +		event_trace_up_ref();					\
> > >  		ret = register_trace_##call(ftrace_profile_##call);	\
> > > +	}								\
> > >  									\
> > >  	return ret;							\
> > >  }									\
> > >  									\
> > >  static void ftrace_profile_disable_##call(struct ftrace_event_call *event_call)\
> > >  {									\
> > > -	if (atomic_add_negative(-1, &event_call->profile_count))	\
> > > +	if (atomic_add_negative(-1, &event_call->profile_count)) {	\
> > >  		unregister_trace_##call(ftrace_profile_##call);		\
> > > +		event_trace_down_ref();					\
> > > +	}								\
> > >  }
> > 
> > Ha, almost, make that {un,}register_ftrace_##call() and stick the module
> > gunk in there, and I'm ok.
> 
> Peter, that {un,}register_tace_##call is the tracepoint code. The 
> DEFINE_TRACE creates those functions. This is the lowest level we can go 
> in the ftrace.h file.

Did you miss the extra f?

You can wrap the regular {un,}register_trace_##call() things in
{un,}register_/F/trace_##call() functions which also take care of the
module stuff.

Your patch is virtually identical to the one that started this thread,
everybody using the TRACE_EVENT() things will still need to worry about
modules.
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