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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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Date: Tue, 25 Aug 2009 12:47:15 +0200
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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...