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

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Message-ID: <CAJZ5v0i-Y9qwKTc=EOOxRGHqMitZpqti6addKPMP45byZ18K5Q@mail.gmail.com>
Date: Fri, 4 Oct 2024 18:28:19 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Lukasz Luba <lukasz.luba@....com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, "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 Fri, Oct 4, 2024 at 3:52 PM Lukasz Luba <lukasz.luba@....com> wrote:
>
>
>
> 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>

Thank you!