[PATCH] class: add a semaphore to struct class, and use that instead of the subsystem rwsem.

This moves us away from using the rwsem, although recursive adds and removes of class devices
is not yet possible (nor is it really known if it even is needed.)  So this simple change is
done instead.
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/class.c

@@ -140,6 +140,7 @@ int class_register(struct class * cls)
 
 	INIT_LIST_HEAD(&cls->children);
 	INIT_LIST_HEAD(&cls->interfaces);
+	init_MUTEX(&cls->sem);
 	error = kobject_set_name(&cls->subsys.kset.kobj, "%s", cls->name);
 	if (error)
 		return error;
@@ -413,12 +414,12 @@ int class_device_add(struct class_device *class_dev)
 
 	/* now take care of our own registration */
 	if (parent) {
-		down_write(&parent->subsys.rwsem);
+		down(&parent->sem);
 		list_add_tail(&class_dev->node, &parent->children);
 		list_for_each_entry(class_intf, &parent->interfaces, node)
 			if (class_intf->add)
 				class_intf->add(class_dev);
-		up_write(&parent->subsys.rwsem);
+		up(&parent->sem);
 	}
 
 	if (MAJOR(class_dev->devt))
@@ -448,12 +449,12 @@ void class_device_del(struct class_device *class_dev)
 	struct class_interface * class_intf;
 
 	if (parent) {
-		down_write(&parent->subsys.rwsem);
+		down(&parent->sem);
 		list_del_init(&class_dev->node);
 		list_for_each_entry(class_intf, &parent->interfaces, node)
 			if (class_intf->remove)
 				class_intf->remove(class_dev);
-		up_write(&parent->subsys.rwsem);
+		up(&parent->sem);
 	}
 
 	if (class_dev->dev)
@@ -509,8 +510,8 @@ void class_device_put(struct class_device *class_dev)
 
 int class_interface_register(struct class_interface *class_intf)
 {
-	struct class * parent;
-	struct class_device * class_dev;
+	struct class *parent;
+	struct class_device *class_dev;
 
 	if (!class_intf || !class_intf->class)
 		return -ENODEV;
@@ -519,14 +520,13 @@ int class_interface_register(struct class_interface *class_intf)
 	if (!parent)
 		return -EINVAL;
 
-	down_write(&parent->subsys.rwsem);
+	down(&parent->sem);
 	list_add_tail(&class_intf->node, &parent->interfaces);
-
 	if (class_intf->add) {
 		list_for_each_entry(class_dev, &parent->children, node)
 			class_intf->add(class_dev);
 	}
-	up_write(&parent->subsys.rwsem);
+	up(&parent->sem);
 
 	return 0;
 }
@@ -539,14 +539,13 @@ void class_interface_unregister(struct class_interface *class_intf)
 	if (!parent)
 		return;
 
-	down_write(&parent->subsys.rwsem);
+	down(&parent->sem);
 	list_del_init(&class_intf->node);
-
 	if (class_intf->remove) {
 		list_for_each_entry(class_dev, &parent->children, node)
 			class_intf->remove(class_dev);
 	}
-	up_write(&parent->subsys.rwsem);
+	up(&parent->sem);
 
 	class_put(parent);
 }

include/linux/device.h

@@ -15,7 +15,6 @@
 #include <linux/ioport.h>
 #include <linux/kobject.h>
 #include <linux/list.h>
-#include <linux/spinlock.h>
 #include <linux/types.h>
 #include <linux/module.h>
 #include <linux/pm.h>
@@ -148,6 +147,7 @@ struct class {
 	struct subsystem	subsys;
 	struct list_head	children;
 	struct list_head	interfaces;
+	struct semaphore	sem;	/* locks both the children and interfaces lists */
 
 	struct class_attribute		* class_attrs;
 	struct class_device_attribute	* class_dev_attrs;