linux-kernel - Re: [PATCH] Module : call synchronize_sched() between module exit() and free.

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Message-Id: <200807301304.51014.rusty@rustcorp.com.au>
Date:	Wed, 30 Jul 2008 13:04:50 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	"Frank Ch. Eigler" <fche@...hat.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] Module : call synchronize_sched() between module exit() and free.

On Wednesday 30 July 2008 12:27:51 Mathieu Desnoyers wrote:
> > Hi Mathieu,
> >
> >    Yes: stop_machine is merely used to atomically check the module
> > refcount for zero and set the state so it can't be incremented again (ie.
> > try_module_get will fail).
> >
> >    So placing a tracepoint or marker in a module does not bump the module
> > refcount?  If that's true, then there needs to be some kind of
> > remove_markers_from_module() call after module->exit(), which should do
> > the synchronize_sched() or whatever, right?
> >
> > Rusty.
>
> Actually, it's not placing a marker/tracepoint in a module which causes
> a problem, this is a simple function call after all, and correctly dealt
> with by current module.c code.
>
> The problem comes from a probe function (the callback) that would be
> registered to be called from a marker and would sit in an unloadable
> kernel module. I would not want to tie the refcount of the probe modules
> to the fact that they are connected to a marker because it would then
> become impossible to unload them due to the fact that unregistration is
> done in module exit().

Hi Mathieu,

    Still confused, sorry.  Why don't you don't do a synchronize_sched() at 
the end of your module's exit routine?  "You must be completely finished by 
the time ->exit() returns" is the rule so far...

Rusty.
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