usb: roles: Improve the fix for a false positive recursive locking complaint

Improve commit fc88bb1 ("usb: roles: add lockdep class key to struct
usb_role_switch") as follows:
* Move the lock class key declaration just above the mutex declaration such
  that the declaration order of these objects matches their initialization
  order.
* Destroy the mutex and lock class key just before these objects are
  freed. This makes it easier to verify that the destruction calls happen
  after the last use of these objects.
* Instead of switching the mutex key to the dynamic lock class key after
  initialization of the mutex has completed, initialize the mutex with the
  dynamic lock class key.

Cc: Amit Sunil Dhamne <[email protected]>
Cc: Badhri Jagan Sridharan <[email protected]>
Cc: Hans de Goede <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Heikki Krogerus <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: bvanassche

drivers/usb/roles/class.c

@@ -22,6 +22,7 @@ static const struct class role_class = {
 
 struct usb_role_switch {
 	struct device dev;
+	struct lock_class_key key;
 	struct mutex lock; /* device lock*/
 	struct module *module; /* the module this device depends on */
 	enum usb_role role;
@@ -34,8 +35,6 @@ struct usb_role_switch {
 	usb_role_switch_set_t set;
 	usb_role_switch_get_t get;
 	bool allow_userspace_control;
-
-	struct lock_class_key key;
 };
 
 #define to_role_switch(d)	container_of(d, struct usb_role_switch, dev)
@@ -329,6 +328,8 @@ static void usb_role_switch_release(struct device *dev)
 {
 	struct usb_role_switch *sw = to_role_switch(dev);
 
+	mutex_destroy(&sw->lock);
+	lockdep_unregister_key(&sw->key);
 	kfree(sw);
 }
 
@@ -367,7 +368,8 @@ usb_role_switch_register(struct device *parent,
 	if (!sw)
 		return ERR_PTR(-ENOMEM);
 
-	mutex_init(&sw->lock);
+	lockdep_register_key(&sw->key);
+	mutex_init_with_key(&sw->lock, &sw->key);
 
 	sw->allow_userspace_control = desc->allow_userspace_control;
 	sw->usb2_port = desc->usb2_port;
@@ -399,9 +401,6 @@ usb_role_switch_register(struct device *parent,
 
 	sw->registered = true;
 
-	lockdep_register_key(&sw->key);
-	lockdep_set_class(&sw->lock, &sw->key);
-
 	/* TODO: Symlinks for the host port and the device controller. */
 
 	return sw;
@@ -418,9 +417,6 @@ void usb_role_switch_unregister(struct usb_role_switch *sw)
 {
 	if (IS_ERR_OR_NULL(sw))
 		return;
-
-	lockdep_unregister_key(&sw->key);
-
 	sw->registered = false;
 	if (dev_fwnode(&sw->dev))
 		component_del(&sw->dev, &connector_ops);