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

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Message-ID: <alpine.DEB.2.00.0908241213060.7587@gandalf.stny.rr.com>
Date:	Mon, 24 Aug 2009 12:13:47 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Ingo Molnar <mingo@...e.hu>, Li Zefan <lizf@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload


On Mon, 24 Aug 2009, Peter Zijlstra wrote:
> > > > > 
> > > > > 
> > > > > Hrmm, feel fragile, why don't we check if all a modules tracepoints are
> > > > > unused on unload?
> > > > > 
> > > > 
> > > > I don't think it's fragile. We are profiling via a module's
> > > > tracepoint, so we should pin the module, via module_get().
> > > > If event->profile_enable() has been calld, we should make
> > > > sure it's profile_disable() will be called.
> > > 
> > > What I call fragile is that everyone registering a tracepoint 
> > > callback will now apparently need to worry about modules, _that_ 
> > > is fragile.
> > > 
> > > Either make module unload look at tracepoint users, or place the 
> > > try_get_module() in the registration hooks so that regular users 
> > > don't need to worry about it.
> > 
> > The bug found by Li needs to be fixed obviously.
> > 
> > I tend to agree with you that this does not appear to be the best 
> > place to do it: so you suggest to implicitly increase the module 
> > refcount on callback registr instead? (and releasing it when 
> > unregistering)
> > 
> > Same end result, slightly cleaner place to bump the refcount.
> 
> Yes, because the user of tracepoints should never need to care about
> modules.

I also agree with Peter on this.

-- Steve

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