linux-kernel - Re: [PATCH V5] thermal: Add cooling device's statistics in sysfs

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Date:   Mon, 13 Aug 2018 19:43:15 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH V5] thermal: Add cooling device's statistics in sysfs

On Monday, 13 August 2018 19:21:43 MSK Viresh Kumar wrote:
> On 13 August 2018 at 21:36, Dmitry Osipenko <digetx@...il.com> wrote:
> > I'm working on adding support of OPP and cooling for NVIDIA Tegra20/30
> > CPUFreq driver and stumbled upon a bug that is introduced by this patch.
> > It is triggered on the driver module unload.
> The problem is that device_unregister() will end up freeing the cdev as
> well, so the current sequence is surely wrong.
> 
> > diff --git a/drivers/thermal/thermal_core.c
> > b/drivers/thermal/thermal_core.c index 6ab982309e6a..de53c821a282 100644
> > --- a/drivers/thermal/thermal_core.c
> > +++ b/drivers/thermal/thermal_core.c
> > @@ -1102,8 +1102,8 @@ void thermal_cooling_device_unregister(struct
> > thermal_cooling_device *cdev)> 
> >         mutex_unlock(&thermal_list_lock);
> >         
> >         ida_simple_remove(&thermal_cdev_ida, cdev->id);
> > 
> > -       device_unregister(&cdev->device);
> > 
> >         thermal_cooling_device_destroy_sysfs(cdev);
> > 
> > +       device_unregister(&cdev->device);
> 
> But this looks wrong as well, as the device is still around while
> memory of its sysfs data is gone.

Indeed.

> Maybe something like this is what we need:
> 
> device_del();
> thermal_cooling_device_destroy_sysfs();
> device_put();

[I just realized that thermal_zone and cooling_device are not interrelated. 
I'm not familiar with the thermal/ code]

Thank you Viresh, your proposal looks good to me and works fine. Will you make 
a proper patch?