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

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Date:   Thu, 19 Jan 2023 17:39:29 +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 16:05, Rafael J. Wysocki wrote:
> On Thu, Jan 19, 2023 at 3:13 PM Daniel Lezcano
> <daniel.lezcano@...aro.org> wrote:
>>
>> 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 ?
> 
> I suppose so.
> 
> And we'd like it to be used some places like
> thermal_zone_device_register_with_trips(), wouldn't we?

Yes, in thermal_zone_device_register_with_trips() and 
thermal_cooling_device_register().



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