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Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Li Zefan <lizf@cn.fujitsu.com>, Steven Rostedt <rostedt@goodmis.org>,
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       LKML <linux-kernel@vger.kernel.org>
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Date: Tue, 25 Aug 2009 12:32:39 +0200
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On Tue, 2009-08-25 at 12:22 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Tue, 2009-08-25 at 11:05 +0200, Ingo Molnar wrote:
> > > * Peter Zijlstra <peterz@infradead.org> wrote:
> > > 
> > > > Ah, my bad, I was thikning tracepoint_probe_register() was the 
> > > > thing that registered the tracepoint itself, not the callback.
> > > > 
> > > > Ok, then what's the problem?, don't do modules that consume their 
> > > > own tracepoints, seems simple enough.
> > > 
> > > is this a reasonable restriction? I dont see any reason why the 
> > > act of defining and providing a tracepoint should be exclusive 
> > > of the ability to make use of it.
> > 
> > It doesn't make sense to me, you don't need your own tracepoints 
> > because you generate the events yourself, you already have them.
> 
> For a reasonable large subsystem/driver i can very well imagine this 
> to happen: why should the subsystem add _another_ layer of callbacks 
> if it can reuse the generic tracepoint code and register itself to 
> those?

Then that subsystem would be non functioning when the kernel is build
without tracepoints.

Nothing should rely on tracepoint being present, they are and should
remain a debug feature, not a core hook thing.

Do you really wish to burden every tracepoint user with the extra logic
needed to deal with modules?