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

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Date:   Fri, 20 Jan 2023 15:13:25 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Zhang, Rui" <rui.zhang@...el.com>
Cc:     "rafael@...nel.org" <rafael@...nel.org>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "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 Fri, Jan 20, 2023 at 3:10 PM Zhang, Rui <rui.zhang@...el.com> wrote:
>
> On Thu, 2023-01-19 at 18:21 +0100, Rafael J. Wysocki wrote:
> > On Thursday, January 19, 2023 5:39:29 PM CET Daniel Lezcano wrote:
> > > 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().
> >
> > Something like the patch below I think, because
> > thermal_cooling_device_register()
> > is a wrapper around thermal_zone_device_register_with_trips().
> >
>
> thermal_zone_device_register() is a wrapper around
> thermal_zone_device_register_with_trips(), but
> thermal_cooling_device_register() is not. :)
>
> thermal_cooling_device_register() registers a cooling device to thermal
> class so the class_is_registered() check is still needed.

OK, thanks!