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Date: Fri, 20 Jan 2023 14:09:36 +0000
From: "Zhang, Rui" <rui.zhang@...el.com>
To: "rafael@...nel.org" <rafael@...nel.org>,
"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
"rjw@...ysocki.net" <rjw@...ysocki.net>
CC: "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, 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.
thanks,
rui
> It needs to be split into 2 individual patches.
>
> ---
> drivers/base/class.c | 16 +++++++++++-----
> drivers/thermal/thermal_core.c | 3 +++
> include/linux/device/class.h | 5 +++++
> 3 files changed, 19 insertions(+), 5 deletions(-)
>
> Index: linux-pm/include/linux/device/class.h
> ===================================================================
> --- linux-pm.orig/include/linux/device/class.h
> +++ linux-pm/include/linux/device/class.h
> @@ -82,6 +82,11 @@ struct class_dev_iter {
> const struct device_type *type;
> };
>
> +static inline bool class_is_registered(struct class *class)
> +{
> + return !!class->p;
> +}
> +
> extern struct kobject *sysfs_dev_block_kobj;
> extern struct kobject *sysfs_dev_char_kobj;
> extern int __must_check __class_register(struct class *class,
> Index: linux-pm/drivers/base/class.c
> ===================================================================
> --- linux-pm.orig/drivers/base/class.c
> +++ linux-pm/drivers/base/class.c
> @@ -53,6 +53,8 @@ static void class_release(struct kobject
>
> pr_debug("class '%s': release.\n", class->name);
>
> + class->p = NULL;
> +
> if (class->class_release)
> class->class_release(class);
> else
> @@ -186,17 +188,21 @@ int __class_register(struct class *cls,
> cls->p = cp;
>
> error = kset_register(&cp->subsys);
> - if (error) {
> - kfree(cp);
> - return error;
> - }
> + if (error)
> + goto err_out;
> +
> error = class_add_groups(class_get(cls), cls->class_groups);
> class_put(cls);
> if (error) {
> kobject_del(&cp->subsys.kobj);
> kfree_const(cp->subsys.kobj.name);
> - kfree(cp);
> + goto err_out;
> }
> + return 0;
> +
> +err_out:
> + cls->p = NULL;
> + kfree(cp);
> return error;
> }
> EXPORT_SYMBOL_GPL(__class_register);
> Index: linux-pm/drivers/thermal/thermal_core.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.c
> +++ linux-pm/drivers/thermal/thermal_core.c
> @@ -1342,6 +1342,9 @@ thermal_zone_device_register_with_trips(
> if (num_trips > 0 && (!ops->get_trip_type || !ops-
> >get_trip_temp) && !trips)
> return ERR_PTR(-EINVAL);
>
> + if (!class_is_registered(&thermal_class))
> + return ERR_PTR(-ENODEV);
> +
> tz = kzalloc(sizeof(*tz), GFP_KERNEL);
> if (!tz)
> return ERR_PTR(-ENOMEM);
>
>
>
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