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

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Date:   Mon, 13 Aug 2018 21:51:43 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
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 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.

Maybe something like this is what we need:

device_del();
thermal_cooling_device_destroy_sysfs();
device_put();

--
viresh