[v1,2/2] thermal: Fail object registration if thermal class is not registered

  From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

If thermal_class is not registered with the driver core, there is no way
to expose the interfaces used by the thermal control framework, so
prevent thermal zones and cooling devices from being registered in
that case by returning an error from object registration functions.

For this purpose, introduce class_is_registered() that checks the
private pointer of the given class and returns 'false' if it is NULL,
which means that the class has not been registered, and use it in the
thermal framework.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/thermal/thermal_core.c |    6 ++++++
 include/linux/device/class.h   |    5 +++++
 2 files changed, 11 insertions(+)
  

On 20/01/2023 20:48, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> If thermal_class is not registered with the driver core, there is no way
> to expose the interfaces used by the thermal control framework, so
> prevent thermal zones and cooling devices from being registered in
> that case by returning an error from object registration functions.
> 
> For this purpose, introduce class_is_registered() that checks the
> private pointer of the given class and returns 'false' if it is NULL,
> which means that the class has not been registered, and use it in the
> thermal framework.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
  

On Fri, Jan 20, 2023 at 08:48:07PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> If thermal_class is not registered with the driver core, there is no way
> to expose the interfaces used by the thermal control framework, so
> prevent thermal zones and cooling devices from being registered in
> that case by returning an error from object registration functions.
> 
> For this purpose, introduce class_is_registered() that checks the
> private pointer of the given class and returns 'false' if it is NULL,
> which means that the class has not been registered, and use it in the
> thermal framework.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/thermal/thermal_core.c |    6 ++++++
>  include/linux/device/class.h   |    5 +++++
>  2 files changed, 11 insertions(+)
> 
> 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;

I really do not like this as it is exposing internals to drivers and
whenever we do that, it gets abused and we have to unwind the mess in a
few years.

Overall, I'm trying to remove the ->p usage, but that's a longterm goal
of mine (to allow class and bus structures to be in read-only memory),
which isn't your issue here, but it's good to think about why you want
to know this information (more below.)

> +}
> +
>  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/thermal/thermal_core.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.c
> +++ linux-pm/drivers/thermal/thermal_core.c
> @@ -880,6 +880,9 @@ __thermal_cooling_device_register(struct
>  	    !ops->set_cur_state)
>  		return ERR_PTR(-EINVAL);
>  
> +	if (!class_is_registered(&thermal_class))
> +		return ERR_PTR(-ENODEV);

If the class isn't registered, then sommething went wrong with the
thermal core code, right?  So why isn't the thermal core keeping a local
variable of "class was registered" and relying on the driver core to
know this?

The number of individual users that should be doing one thing or another
if a class is not registered feels very very slim.  How come this code
is being called at all if the thermal class was not registered in the
first place?  What would have prevented that from happening?  Is it an
ordering issue, or a kernel configuration issue?

thanks,

greg k-h
  

On Sat, Jan 21, 2023 at 8:40 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Fri, Jan 20, 2023 at 08:48:07PM +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > If thermal_class is not registered with the driver core, there is no way
> > to expose the interfaces used by the thermal control framework, so
> > prevent thermal zones and cooling devices from being registered in
> > that case by returning an error from object registration functions.
> >
> > For this purpose, introduce class_is_registered() that checks the
> > private pointer of the given class and returns 'false' if it is NULL,
> > which means that the class has not been registered, and use it in the
> > thermal framework.
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >  drivers/thermal/thermal_core.c |    6 ++++++
> >  include/linux/device/class.h   |    5 +++++
> >  2 files changed, 11 insertions(+)
> >
> > 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;
>
> I really do not like this as it is exposing internals to drivers and
> whenever we do that, it gets abused and we have to unwind the mess in a
> few years.
>
> Overall, I'm trying to remove the ->p usage, but that's a longterm goal
> of mine (to allow class and bus structures to be in read-only memory),
> which isn't your issue here, but it's good to think about why you want
> to know this information (more below.)
>
> > +}
> > +
> >  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/thermal/thermal_core.c
> > ===================================================================
> > --- linux-pm.orig/drivers/thermal/thermal_core.c
> > +++ linux-pm/drivers/thermal/thermal_core.c
> > @@ -880,6 +880,9 @@ __thermal_cooling_device_register(struct
> >           !ops->set_cur_state)
> >               return ERR_PTR(-EINVAL);
> >
> > +     if (!class_is_registered(&thermal_class))
> > +             return ERR_PTR(-ENODEV);
>
> If the class isn't registered, then sommething went wrong with the
> thermal core code, right?  So why isn't the thermal core keeping a local
> variable of "class was registered" and relying on the driver core to
> know this?
>
> The number of individual users that should be doing one thing or another
> if a class is not registered feels very very slim.  How come this code
> is being called at all if the thermal class was not registered in the
> first place?  What would have prevented that from happening?  Is it an
> ordering issue, or a kernel configuration issue?

It's basically a matter of class_register() returning an error.

Yes, we could use an extra variable for this purpose, but that would
be a bit wasteful, because thermal_class will then sit unused and
occupy memory in vain.

Oh well, we may as well just allocate it dynamically.
  

On Mon, Jan 23, 2023 at 09:16:33PM +0100, Rafael J. Wysocki wrote:
> On Sat, Jan 21, 2023 at 8:40 AM Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > On Fri, Jan 20, 2023 at 08:48:07PM +0100, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > >
> > > If thermal_class is not registered with the driver core, there is no way
> > > to expose the interfaces used by the thermal control framework, so
> > > prevent thermal zones and cooling devices from being registered in
> > > that case by returning an error from object registration functions.
> > >
> > > For this purpose, introduce class_is_registered() that checks the
> > > private pointer of the given class and returns 'false' if it is NULL,
> > > which means that the class has not been registered, and use it in the
> > > thermal framework.
> > >
> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > ---
> > >  drivers/thermal/thermal_core.c |    6 ++++++
> > >  include/linux/device/class.h   |    5 +++++
> > >  2 files changed, 11 insertions(+)
> > >
> > > 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;
> >
> > I really do not like this as it is exposing internals to drivers and
> > whenever we do that, it gets abused and we have to unwind the mess in a
> > few years.
> >
> > Overall, I'm trying to remove the ->p usage, but that's a longterm goal
> > of mine (to allow class and bus structures to be in read-only memory),
> > which isn't your issue here, but it's good to think about why you want
> > to know this information (more below.)
> >
> > > +}
> > > +
> > >  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/thermal/thermal_core.c
> > > ===================================================================
> > > --- linux-pm.orig/drivers/thermal/thermal_core.c
> > > +++ linux-pm/drivers/thermal/thermal_core.c
> > > @@ -880,6 +880,9 @@ __thermal_cooling_device_register(struct
> > >           !ops->set_cur_state)
> > >               return ERR_PTR(-EINVAL);
> > >
> > > +     if (!class_is_registered(&thermal_class))
> > > +             return ERR_PTR(-ENODEV);
> >
> > If the class isn't registered, then sommething went wrong with the
> > thermal core code, right?  So why isn't the thermal core keeping a local
> > variable of "class was registered" and relying on the driver core to
> > know this?
> >
> > The number of individual users that should be doing one thing or another
> > if a class is not registered feels very very slim.  How come this code
> > is being called at all if the thermal class was not registered in the
> > first place?  What would have prevented that from happening?  Is it an
> > ordering issue, or a kernel configuration issue?
> 
> It's basically a matter of class_register() returning an error.

Ok, so not a real problem then :)

> Yes, we could use an extra variable for this purpose, but that would
> be a bit wasteful, because thermal_class will then sit unused and
> occupy memory in vain.

How would it retain memory if class_register() failed?

> Oh well, we may as well just allocate it dynamically.

Allocate what?

confused,

greg k-h
  

On Tue, Jan 24, 2023 at 7:03 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Mon, Jan 23, 2023 at 09:16:33PM +0100, Rafael J. Wysocki wrote:
> > On Sat, Jan 21, 2023 at 8:40 AM Greg Kroah-Hartman
> > <gregkh@linuxfoundation.org> wrote:
> > >
> > > On Fri, Jan 20, 2023 at 08:48:07PM +0100, Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > >
> > > > If thermal_class is not registered with the driver core, there is no way
> > > > to expose the interfaces used by the thermal control framework, so
> > > > prevent thermal zones and cooling devices from being registered in
> > > > that case by returning an error from object registration functions.
> > > >
> > > > For this purpose, introduce class_is_registered() that checks the
> > > > private pointer of the given class and returns 'false' if it is NULL,
> > > > which means that the class has not been registered, and use it in the
> > > > thermal framework.
> > > >
> > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > > ---
> > > >  drivers/thermal/thermal_core.c |    6 ++++++
> > > >  include/linux/device/class.h   |    5 +++++
> > > >  2 files changed, 11 insertions(+)
> > > >
> > > > 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;
> > >
> > > I really do not like this as it is exposing internals to drivers and
> > > whenever we do that, it gets abused and we have to unwind the mess in a
> > > few years.
> > >
> > > Overall, I'm trying to remove the ->p usage, but that's a longterm goal
> > > of mine (to allow class and bus structures to be in read-only memory),
> > > which isn't your issue here, but it's good to think about why you want
> > > to know this information (more below.)
> > >
> > > > +}
> > > > +
> > > >  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/thermal/thermal_core.c
> > > > ===================================================================
> > > > --- linux-pm.orig/drivers/thermal/thermal_core.c
> > > > +++ linux-pm/drivers/thermal/thermal_core.c
> > > > @@ -880,6 +880,9 @@ __thermal_cooling_device_register(struct
> > > >           !ops->set_cur_state)
> > > >               return ERR_PTR(-EINVAL);
> > > >
> > > > +     if (!class_is_registered(&thermal_class))
> > > > +             return ERR_PTR(-ENODEV);
> > >
> > > If the class isn't registered, then sommething went wrong with the
> > > thermal core code, right?  So why isn't the thermal core keeping a local
> > > variable of "class was registered" and relying on the driver core to
> > > know this?
> > >
> > > The number of individual users that should be doing one thing or another
> > > if a class is not registered feels very very slim.  How come this code
> > > is being called at all if the thermal class was not registered in the
> > > first place?  What would have prevented that from happening?  Is it an
> > > ordering issue, or a kernel configuration issue?
> >
> > It's basically a matter of class_register() returning an error.
>
> Ok, so not a real problem then :)
>
> > Yes, we could use an extra variable for this purpose, but that would
> > be a bit wasteful, because thermal_class will then sit unused and
> > occupy memory in vain.
>
> How would it retain memory if class_register() failed?

The point was that we might use the existing (but not registered)
class object to "flag" the fact that the class could not be used
without adding extra variables.

> > Oh well, we may as well just allocate it dynamically.
>
> Allocate what?

Well, that was a bit terse, sorry.

This patch implements what I meant:
https://patchwork.kernel.org/project/linux-pm/patch/5660360.DvuYhMxLoT@kreacher/
  

On Tue, Jan 24, 2023 at 02:57:55PM +0100, Rafael J. Wysocki wrote:
> On Tue, Jan 24, 2023 at 7:03 AM Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> 
> > > Oh well, we may as well just allocate it dynamically.
> >
> > Allocate what?
> 
> Well, that was a bit terse, sorry.
> 
> This patch implements what I meant:
> https://patchwork.kernel.org/project/linux-pm/patch/5660360.DvuYhMxLoT@kreacher/

That looks good, I like that change, it's much simpler overall.

greg k-h