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

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Message-ID: <CAJZ5v0icp3nH+3-timEh2o8kxXpe4O2uMdJ8pSwe8fmY_OW4zA@mail.gmail.com>
Date:   Thu, 19 Jan 2023 16:05:09 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "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 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?