software node: Handle software node injection to an existing device properly

The function software_node_notify() - the function that creates
and removes the symlinks between the node and the device - was
called unconditionally in device_add_software_node() and
device_remove_software_node(), but it needs to be called in
those functions only in the special case where the node is
added to a device that has already been registered.

This fixes NULL pointer dereference that happens if
device_remove_software_node() is used with device that was
never registered.

Fixes: b622b245 ("software node: Allow node addition to already existing device")
Reported-and-tested-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/swnode.c

@@ -1045,6 +1045,14 @@ int device_add_software_node(struct device *dev, const struct software_node *nod
 	}
 
 	set_secondary_fwnode(dev, &swnode->fwnode);
+
+	/*
+	 * If the device has been fully registered by the time this function is
+	 * called, software_node_notify() must be called separately so that the
+	 * symlinks get created and the reference count of the node is kept in
+	 * balance.
+	 */
+	if (device_is_registered(dev))
 		software_node_notify(dev, KOBJ_ADD);
 
 	return 0;
@@ -1065,6 +1073,7 @@ void device_remove_software_node(struct device *dev)
 	if (!swnode)
 		return;
 
+	if (device_is_registered(dev))
 		software_node_notify(dev, KOBJ_REMOVE);
 	set_secondary_fwnode(dev, NULL);
 	kobject_put(&swnode->kobj);
@@ -1119,8 +1128,7 @@ int software_node_notify(struct device *dev, unsigned long action)
 
 	switch (action) {
 	case KOBJ_ADD:
-		ret = sysfs_create_link_nowarn(&dev->kobj, &swnode->kobj,
-					       "software_node");
+		ret = sysfs_create_link(&dev->kobj, &swnode->kobj, "software_node");
 		if (ret)
 			break;