linux-kernel - Re: [PATCH 2/3] tracing/profile: add ref count for registering profile events

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Date:	Fri, 11 Sep 2009 16:09:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Subject: Re: [PATCH 2/3] tracing/profile: add ref count for registering
 profile events

On Fri, 2009-09-11 at 16:04 +0200, Peter Zijlstra wrote:
> On Fri, 2009-09-11 at 09:54 -0400, Steven Rostedt wrote:
> 
> > +#ifdef MODULE
> > +# define event_trace_up_ref()					\
> > +	do {							\
> > +		if (!try_module_get(THIS_MODULE)) {		\
> > +			atomic_dec(&event_call->profile_count);	\
> > +			return -ENOENT;				\
> > +		}						\
> > +	} while (0)
> > +# define event_trace_down_ref() module_put(THIS_MODULE)
> > +#else
> > +# define event_trace_up_ref() do { } while (0)
> > +# define event_trace_down_ref() do { } while (0)
> > +#endif
> 
> That's like truely gruesomely ugly.
> 
> At the very least write it like:
> 
> int event_trace_up_ref(struct ftrace_event_call *call)
> {
> 	if (!try_module_get(THIS_MODULE)) {
> 		atomic_dev(&call->profile_count);
> 		return -ENOENT;
> 	}
> 	return 0;
> }

Or we can go with Li's original patch, that was less ugly.

I still think tracepoints/markers should sort this out, because we now
have a sematic difference between the two wrt modules.



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