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

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Message-Id: <1251197235.7538.1142.camel@twins>
Date:	Tue, 25 Aug 2009 12:47:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload

On Tue, 2009-08-25 at 12:39 +0200, Ingo Molnar wrote:

> > Do you really wish to burden every tracepoint user with the extra 
> > logic needed to deal with modules?
> 
> Not necessarily - i'm just outlining why i think that the 'dont 
> allow subsystems to utilize tracepoint callbacks' is a restriction 
> we should not live with voluntarily.

Well, unless someone has a bright idea that's what it comes down to. And
not having to care about modules when using tracepoint wins hands down
for me.

The issue seems rather simple:

Either we force everybody who uses a tracepoint to care about modules,
be this by having to do try_get_module() themselves or by having to
listen to some notifier and have their callback forcibly dropped on
unload -- both suck IMO, suck very hard indeed.

Or by having modules that use their own tracepoint be stuck, because
once you block unlock when a tracepoint has callbacks, and it installed
a callback on itself, its not going to go away.

And since I don't care about modules at all and really wish they'd never
been invented...
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