[PATCH] sysdev: remove the rwsem usage from this subsystem.

If further finer grained locking is needed, we can add a lock to the sysdev_class to
lock the class drivers list.  But if you do that, remember the global list also is still
there and needs to be protected.  That's why I went with a simple lock for everything.
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/sys.c

@@ -103,6 +103,7 @@ EXPORT_SYMBOL_GPL(sysdev_class_unregister);
 
 
 static LIST_HEAD(sysdev_drivers);
+static DECLARE_MUTEX(sysdev_drivers_lock);
 
 /**
  *	sysdev_driver_register - Register auxillary driver
@@ -119,7 +120,7 @@ static LIST_HEAD(sysdev_drivers);
 int sysdev_driver_register(struct sysdev_class * cls,
 			   struct sysdev_driver * drv)
 {
-	down_write(&system_subsys.rwsem);
+	down(&sysdev_drivers_lock);
 	if (cls && kset_get(&cls->kset)) {
 		list_add_tail(&drv->entry, &cls->drivers);
 
@@ -131,7 +132,7 @@ int sysdev_driver_register(struct sysdev_class * cls,
 		}
 	} else
 		list_add_tail(&drv->entry, &sysdev_drivers);
-	up_write(&system_subsys.rwsem);
+	up(&sysdev_drivers_lock);
 	return 0;
 }
 
@@ -144,7 +145,7 @@ int sysdev_driver_register(struct sysdev_class * cls,
 void sysdev_driver_unregister(struct sysdev_class * cls,
 			      struct sysdev_driver * drv)
 {
-	down_write(&system_subsys.rwsem);
+	down(&sysdev_drivers_lock);
 	list_del_init(&drv->entry);
 	if (cls) {
 		if (drv->remove) {
@@ -154,7 +155,7 @@ void sysdev_driver_unregister(struct sysdev_class * cls,
 		}
 		kset_put(&cls->kset);
 	}
-	up_write(&system_subsys.rwsem);
+	up(&sysdev_drivers_lock);
 }
 
 EXPORT_SYMBOL_GPL(sysdev_driver_register);
@@ -193,7 +194,7 @@ int sysdev_register(struct sys_device * sysdev)
 	if (!error) {
 		struct sysdev_driver * drv;
 
-		down_write(&system_subsys.rwsem);
+		down(&sysdev_drivers_lock);
 		/* Generic notification is implicit, because it's that
 		 * code that should have called us.
 		 */
@@ -209,7 +210,7 @@ int sysdev_register(struct sys_device * sysdev)
 			if (drv->add)
 				drv->add(sysdev);
 		}
-		up_write(&system_subsys.rwsem);
+		up(&sysdev_drivers_lock);
 	}
 	return error;
 }
@@ -218,7 +219,7 @@ void sysdev_unregister(struct sys_device * sysdev)
 {
 	struct sysdev_driver * drv;
 
-	down_write(&system_subsys.rwsem);
+	down(&sysdev_drivers_lock);
 	list_for_each_entry(drv, &sysdev_drivers, entry) {
 		if (drv->remove)
 			drv->remove(sysdev);
@@ -228,7 +229,7 @@ void sysdev_unregister(struct sys_device * sysdev)
 		if (drv->remove)
 			drv->remove(sysdev);
 	}
-	up_write(&system_subsys.rwsem);
+	up(&sysdev_drivers_lock);
 
 	kobject_unregister(&sysdev->kobj);
 }
@@ -255,7 +256,7 @@ void sysdev_shutdown(void)
 
 	pr_debug("Shutting Down System Devices\n");
 
-	down_write(&system_subsys.rwsem);
+	down(&sysdev_drivers_lock);
 	list_for_each_entry_reverse(cls, &system_subsys.kset.list,
 				    kset.kobj.entry) {
 		struct sys_device * sysdev;
@@ -284,7 +285,7 @@ void sysdev_shutdown(void)
 				cls->shutdown(sysdev);
 		}
 	}
-	up_write(&system_subsys.rwsem);
+	up(&sysdev_drivers_lock);
 }