[PATCH v2] thermal: Fail object registration if thermal class is not registered

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

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, use a thermal_class pointer that will be NULL if the
class is not registered.  To avoid wasting memory in that case, allocate
the thermal class object dynamically and if it fails to register, free
it and clear the thermal_class pointer to NULL.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

-> v2: This replaces the series at
       https://lore.kernel.org/linux-pm/5905717.lOV4Wx5bFT@kreacher/

---
 drivers/thermal/thermal_core.c |   31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

Index: linux-pm/drivers/thermal/thermal_core.c
===================================================================
--- linux-pm.orig/drivers/thermal/thermal_core.c
+++ linux-pm/drivers/thermal/thermal_core.c
@@ -774,10 +774,7 @@ static void thermal_release(struct devic
 	}
 }
 
-static struct class thermal_class = {
-	.name = "thermal",
-	.dev_release = thermal_release,
-};
+static struct class *thermal_class;
 
 static inline
 void print_bind_err_msg(struct thermal_zone_device *tz,
@@ -880,6 +877,9 @@ __thermal_cooling_device_register(struct
 	    !ops->set_cur_state)
 		return ERR_PTR(-EINVAL);
 
+	if (!thermal_class)
+		return ERR_PTR(-ENODEV);
+
 	cdev = kzalloc(sizeof(*cdev), GFP_KERNEL);
 	if (!cdev)
 		return ERR_PTR(-ENOMEM);
@@ -901,7 +901,7 @@ __thermal_cooling_device_register(struct
 	cdev->np = np;
 	cdev->ops = ops;
 	cdev->updated = false;
-	cdev->device.class = &thermal_class;
+	cdev->device.class = thermal_class;
 	cdev->devdata = devdata;
 
 	ret = cdev->ops->get_max_state(cdev, &cdev->max_state);
@@ -1349,6 +1349,9 @@ thermal_zone_device_register_with_trips(
 	if (num_trips > 0 && (!ops->get_trip_type || !ops->get_trip_temp) && !trips)
 		return ERR_PTR(-EINVAL);
 
+	if (!thermal_class)
+		return ERR_PTR(-ENODEV);
+
 	tz = kzalloc(sizeof(*tz), GFP_KERNEL);
 	if (!tz)
 		return ERR_PTR(-ENOMEM);
@@ -1370,7 +1373,7 @@ thermal_zone_device_register_with_trips(
 
 	tz->ops = ops;
 	tz->tzp = tzp;
-	tz->device.class = &thermal_class;
+	tz->device.class = thermal_class;
 	tz->devdata = devdata;
 	tz->trips = trips;
 	tz->num_trips = num_trips;
@@ -1615,9 +1618,21 @@ static int __init thermal_init(void)
 	if (result)
 		goto error;
 
-	result = class_register(&thermal_class);
-	if (result)
+	thermal_class = kzalloc(sizeof(*thermal_class), GFP_KERNEL);
+	if (!thermal_class) {
+		result = -ENOMEM;
+		goto unregister_governors;
+	}
+
+	thermal_class->name = "thermal";
+	thermal_class->dev_release = thermal_release;
+
+	result = class_register(thermal_class);
+	if (result) {
+		kfree(thermal_class);
+		thermal_class = NULL;
 		goto unregister_governors;
+	}
 
 	result = register_pm_notifier(&thermal_pm_nb);
 	if (result)