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

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Message-ID: <20080730040518.GA20490@Krystal>
Date:	Wed, 30 Jul 2008 00:05:18 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Rusty Russell <rusty@...tcorp.com.au>
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.

* Rusty Russell (rusty@...tcorp.com.au) wrote:
> 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...
> 

Hi Rusty,

Yes, this is I think the right solution. Sorry for the title of the
previous email : I started writing a patch and changed my mind half-way.
Doing a synchronize_sched() at the end of the exit() function seems like
the right thing to do. I'll have to update the documentation and
examples accordingly.

Thanks,

Mathieu

> Rusty.

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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