linux-kernel - Re: [PATCH 3/5] thermal/core: Remove unneeded mutex

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Message-ID: <1313b9b6-45f0-aad1-9a3f-c5e1e3636697@linaro.org>
Date:   Thu, 19 Jan 2023 15:13:46 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Zhang, Rui" <rui.zhang@...el.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "amitk@...nel.org" <amitk@...nel.org>
Subject: Re: [PATCH 3/5] thermal/core: Remove unneeded mutex_destroy()

On 19/01/2023 14:24, Rafael J. Wysocki wrote:
> On Thu, Jan 19, 2023 at 1:48 PM Daniel Lezcano
> <daniel.lezcano@...aro.org> wrote:
>>
>> On 19/01/2023 13:11, Rafael J. Wysocki wrote:
>>> On Thu, Jan 19, 2023 at 10:30 AM Daniel Lezcano
>>> <daniel.lezcano@...aro.org> wrote:
>>>>
>>>> On 19/01/2023 08:41, Zhang, Rui wrote:
>>>>> On Wed, 2023-01-18 at 22:11 +0100, Daniel Lezcano wrote:
>>>>>> If the thermal framework fails to initialize, the mutex can be used
>>>>>> by
>>>>>> the different functions registering a thermal zone anyway.
>>>>>
>>>>> Hmm, even with no governors and unregistered thermal sysfs class?
>>>>>
>>>>> IMO, thermal APIs for registering a thermal_zone/cooling_device should
>>>>> yield early if thermal_init fails.
>>>>> For other APIs that relies on a valid
>>>>> thermal_zone_device/thermal_cooling_device pointer, nothing needs to
>>>>> be changed.
>>>>>
>>>>> what do you think?
>>>>
>>>> I think you are right.
>>>>
>>>> It would be nice if we can check if the thermal class is registered and
>>>> bail out if not. But there is no function to check that AFAICS.
>>>>
>>>> Alternatively we can convert the thermal class static structure to a
>>>> pointer and set it to NULL in case of error in thermal_init() ?
>>>
>>> It doesn't matter if this is a NULL pointer or a static object that's
>>> clearly marked as unused.
>>
>> Without introducing another global variable, is it possible to know if
>> the class is used or not ?
> 
> If thermal_class.p is cleared to NULL on class_register() failures in
> thermal_init() (unfortunately, the driver core doesn't do that, but
> maybe it should - let me cut a patch for that), then it can be used
> for that.

It should be in class_unregister() too, right ?

And is it possible to add a class_is_registered() ? in order to prevent 
accessing class structure internals ?

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