cpuidle: Fail cpuidle device registration if there is one already

Refuse to register a cpuidle device if the given CPU has a cpuidle
device already and print a message regarding it.

Without this, an attempt to register a new cpuidle device without
unregistering the existing one leads to the removal of the existing
cpuidle device without removing its sysfs interface.

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

Author: rafaeljw

drivers/cpuidle/cpuidle.c

@@ -635,8 +635,14 @@ static void __cpuidle_device_init(struct cpuidle_device *dev)
 static int __cpuidle_register_device(struct cpuidle_device *dev)
 {
 	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
+	unsigned int cpu = dev->cpu;
 	int i, ret;
 
+	if (per_cpu(cpuidle_devices, cpu)) {
+		pr_info("CPU%d: cpuidle device already registered\n", cpu);
+		return -EEXIST;
+	}
+
 	if (!try_module_get(drv->owner))
 		return -EINVAL;
 
@@ -648,7 +654,7 @@ static int __cpuidle_register_device(struct cpuidle_device *dev)
 			dev->states_usage[i].disable |= CPUIDLE_STATE_DISABLED_BY_USER;
 	}
 
-	per_cpu(cpuidle_devices, dev->cpu) = dev;
+	per_cpu(cpuidle_devices, cpu) = dev;
 	list_add(&dev->device_list, &cpuidle_detected_devices);
 
 	ret = cpuidle_coupled_register_device(dev);