Re: [PATCH 3/5] thermal/core: Remove unneeded mutex_destroy()

["Zhang, Rui" <rui.zhang@intel.com>]

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@linaro.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@linaro.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@linaro.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);
> 
> 
>