linux-kernel - Re: [PATCH v2 3/3] thermal: Make THERMAL

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Date:	Tue, 26 Apr 2011 14:00:31 -0700
From:	Guenter Roeck <guenter.roeck@...csson.com>
To:	Jean Delvare <khali@...ux-fr.org>
CC:	Len Brown <len.brown@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Rene Herman <rene.herman@...il.com>
Subject: Re: [PATCH v2 3/3] thermal: Make THERMAL_HWMON implementation
 fully internal

On Tue, 2011-04-26 at 15:39 -0400, Jean Delvare wrote:
> Hi Guenter,
> 
> On Tue, 26 Apr 2011 10:43:32 -0700, Guenter Roeck wrote:
> > On Tue, 2011-04-26 at 12:29 -0400, Jean Delvare wrote:
> > > On Tue, 26 Apr 2011 08:52:12 -0700, Guenter Roeck wrote:
> > > > On Tue, Apr 26, 2011 at 11:04:07AM -0400, Jean Delvare wrote:
> > > > > * Removal code path is untested, as I have never been able to unload
> > > > > the thermal_sys module on any of my systems. Something is pinning it
> > > > > and I have no idea what it is.
> > > > > 
> > > > Doesn't lsmod show the culprit ?
> > > 
> > > No, it's not a module dependency. The reference counter is set to 1,
> 
> Sorry I realize I have been inaccurate. thermal_sys indeed depends on
> the processor module, and that's what prevents me from unloading it.
> It's the processor module which has a reference count of 1, and no
> dependency, so I have no idea how I could unload it.
> 
You mean the ACPI processor driver ? This comment might explain it:

/*
 * We keep the driver loaded even when ACPI is not running.
 * This is needed for the powernow-k8 driver, that works even without
 * ACPI, but needs symbols from this driver
 */

> > > so somewhere in the kernel something is taking a reference to the
> > > module and won't release it. I wish this was better instrumented so
> > > that it would be possible to know who is doing that.
> > 
> > The most likely culprit seems to be acpi.
> 
> I'm not sure. I don't see any relevant call to try_module_get under
> drivers/acpi, and I'm not aware of any other way to increase the
> reference count.
> 
What happens if the calling code (such as, in my case here, the acpi
video code) gets built into the kernel ? Would that force the module to
be and remain loaded ?

Guenter


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