driver core: bus: move lock_class_key into dynamic structure

Move the lock_class_key structure out of struct bus_type and into the
dynamic structure we create already for all bus_types registered with
the kernel.  This saves on static space and removes one more writable
field in struct bus_type.

In the future, the same field can be moved out of the struct class logic
because it shares this same private structure.

Most everyone will never notice this change, as lockdep is not enabled
in real systems so no memory or logic changes are happening for them.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230201083349.4038660-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/base.h

@@ -52,6 +52,8 @@ struct subsys_private {
 
 	struct kset glue_dirs;
 	struct class *class;
+
+	struct lock_class_key lock_key;
 };
 #define to_subsys_private(obj) container_of_const(obj, struct subsys_private, subsys.kobj)
 

drivers/base/bus.c

@@ -154,6 +154,7 @@ static void bus_release(struct kobject *kobj)
 	struct subsys_private *priv = to_subsys_private(kobj);
 	struct bus_type *bus = priv->bus;
 
+	lockdep_unregister_key(&priv->lock_key);
 	kfree(priv);
 	bus->p = NULL;
 }
@@ -743,7 +744,7 @@ int bus_register(struct bus_type *bus)
 {
 	int retval;
 	struct subsys_private *priv;
-	struct lock_class_key *key = &bus->lock_key;
+	struct lock_class_key *key;
 
 	priv = kzalloc(sizeof(struct subsys_private), GFP_KERNEL);
 	if (!priv)
@@ -785,6 +786,8 @@ int bus_register(struct bus_type *bus)
 	}
 
 	INIT_LIST_HEAD(&priv->interfaces);
+	key = &priv->lock_key;
+	lockdep_register_key(key);
 	__mutex_init(&priv->mutex, "subsys mutex", key);
 	klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);
 	klist_init(&priv->klist_drivers, NULL, NULL);

include/linux/device/bus.h

@@ -112,7 +112,6 @@ struct bus_type {
 	const struct iommu_ops *iommu_ops;
 
 	struct subsys_private *p;
-	struct lock_class_key lock_key;
 
 	bool need_parent_lock;
 };