linux-kernel - Re: [PATCH v2 1/2] thermal: core: Reference count the zone in thermal_zone_get_by

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Message-ID: <a42ebcff-10f8-4888-a3d8-fd2705da41b3@arm.com>
Date: Fri, 4 Oct 2024 14:53:03 +0100
From: Lukasz Luba <lukasz.luba@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v2 1/2] thermal: core: Reference count the zone in
 thermal_zone_get_by_id()



On 10/4/24 14:48, Rafael J. Wysocki wrote:
> On Fri, Oct 4, 2024 at 3:43 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>>
>> On Fri, Oct 4, 2024 at 3:37 PM Lukasz Luba <lukasz.luba@....com> wrote:
>>>
>>>
>>>
>>> On 10/4/24 14:25, Rafael J. Wysocki wrote:
>>>> Hi Łukasz,
>>>>
>>>> On Fri, Oct 4, 2024 at 10:01 AM Lukasz Luba <lukasz.luba@....com> wrote:
>>>>>
>>>>> Hi Rafael,
>>>>>
>>>>> On 10/3/24 13:25, Rafael J. Wysocki wrote:
>>>>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>>>>

[snip]

>>>>>>
>>>>>
>>>>> I wasn't aware of that helpers in cleanup.h.
>>>>>
>>>>> Could you help me to understand when this this
>>>>> 'if (_T) put_device((&_T->device)' will be called?
>>>>
>>>> When the pointer variable initialized via the CLASS() macro goes out
>>>> of scope (that is, before freeing the memory occupied by the pointer
>>>> itself).
>>>
>>>
>>> OK, so do we still need the old code in
>>> thermal_zone_device_unregister(), which calls
>>> put_device(&tz->device) ?
>>
>> Yes, we do.
>>
>>> Maybe that code can go away?
>>
>> That particular one drops the reference acquired by device_register()
>> and I don't see an alternative clean way to drop it.
> 
> The problem there is that local variable tz goes out of scope at the
> end of the function (at least formally) and put_device(&tz->device)
> needs to be called before the wait_for_completion(&tz->removal) which
> definitely needs tz to be still around.

OK, I see now. That makes sense. With that feel free to add:

Reviewed-by: Lukasz Luba <lukasz.luba@....com>