powercap: fix race condition in register_control_type()

The device becomes visible to userspace via device_register()
even before it fully initialized by idr_init(). If userspace
or another thread tries to register a zone immediately after
device_register(), the control_type_valid() will fail because
the control_type is not yet in the list. The IDR is not yet
initialized, so this race condition causes zone registration
failure.

Move idr_init() and list addition before device_register()
fix the race condition.

Signed-off-by: Sumeet Pawnikar <[e-mail]>
[ rjw: Subject adjustment, empty line added ]
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/powercap/powercap_sys.c

···
 	INIT_LIST_HEAD(&control_type->node);
 	control_type->dev.class = &powercap_class;
 	dev_set_name(&control_type->dev, "%s", name);
-	result = device_register(&control_type->dev);
-	if (result) {
-		put_device(&control_type->dev);
-		return ERR_PTR(result);
-	}
 	idr_init(&control_type->idr);
 
 	mutex_lock(&powercap_cntrl_list_lock);
 	list_add_tail(&control_type->node, &powercap_cntrl_list);
 	mutex_unlock(&powercap_cntrl_list_lock);
+
+	result = device_register(&control_type->dev);
+	if (result) {
+		mutex_lock(&powercap_cntrl_list_lock);
+		list_del(&control_type->node);
+		mutex_unlock(&powercap_cntrl_list_lock);
+
+		idr_destroy(&control_type->idr);
+		put_device(&control_type->dev);
+		return ERR_PTR(result);
+	}
 
 	return control_type;
 }