Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload

[Steven Rostedt]

On Thu, 27 Aug 2009, Peter Zijlstra wrote:

> 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?

I thought that was a typo since there is no register_ftrace_##call.

> 
> 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.

Oh, you mean you want me to create a wrapper for it? Note, this does not
affect the normal trace "enable" code, because there's a module call back 
in trace_events.c that disables all the trace points in a module before 
unloading. And this in turn will unregister all events.

> 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.

That's not true. You are not using the TRACE_EVENT, you are modifying the 
TRACE_EVENT. That is different. I don't see how a user could hit this 
issue. You hit it because you modified what was in ftrace.h, and that does 
not count as a user. That's a developer ;-)

-- Steve

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