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

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Message-ID: <CAJZ5v0gR-Z1DNcpRCkK6KapjU_F87RZKpE0ssQn1Y5BiH+sG_g@mail.gmail.com>
Date:   Thu, 19 Jan 2023 14:24:34 +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 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.