Kobject: make kobject apis more robust in handling NULL pointers

It should be ok to pass in NULL for some kobject functions, so add error
checking for all exported kobject functions to be more robust.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

lib/kobject.c

@@ -126,6 +126,8 @@ EXPORT_SYMBOL_GPL(kobject_get_path);
  */
 void kobject_init(struct kobject * kobj)
 {
+	if (!kobj)
+		return;
 	kref_init(&kobj->kref);
 	INIT_LIST_HEAD(&kobj->entry);
 	init_waitqueue_head(&kobj->poll);
@@ -366,6 +368,8 @@ out:
 
 void kobject_del(struct kobject * kobj)
 {
+	if (!kobj)
+		return;
 	sysfs_remove_dir(kobj);
 	unlink(kobj);
 }
@@ -377,6 +381,8 @@ void kobject_del(struct kobject * kobj)
 
 void kobject_unregister(struct kobject * kobj)
 {
+	if (!kobj)
+		return;
 	pr_debug("kobject %s: unregistering\n",kobject_name(kobj));
 	kobject_uevent(kobj, KOBJ_REMOVE);
 	kobject_del(kobj);
@@ -523,6 +529,8 @@ int kset_add(struct kset * k)
 
 int kset_register(struct kset * k)
 {
+	if (!k)
+		return -EINVAL;
 	kset_init(k);
 	return kset_add(k);
 }
@@ -535,6 +543,8 @@ int kset_register(struct kset * k)
 
 void kset_unregister(struct kset * k)
 {
+	if (!k)
+		return;
 	kobject_unregister(&k->kobj);
 }
 
@@ -586,6 +596,9 @@ int subsystem_register(struct subsystem * s)
 {
 	int error;
 
+	if (!s)
+		return -EINVAL;
+
 	subsystem_init(s);
 	pr_debug("subsystem %s: registering\n",s->kset.kobj.name);
 
@@ -598,6 +611,8 @@ int subsystem_register(struct subsystem * s)
 
 void subsystem_unregister(struct subsystem * s)
 {
+	if (!s)
+		return;
 	pr_debug("subsystem %s: unregistering\n",s->kset.kobj.name);
 	kset_unregister(&s->kset);
 }
@@ -612,6 +627,10 @@ void subsystem_unregister(struct subsystem * s)
 int subsys_create_file(struct subsystem * s, struct subsys_attribute * a)
 {
 	int error = 0;
+
+	if (!s || !a)
+		return -EINVAL;
+
 	if (subsys_get(s)) {
 		error = sysfs_create_file(&s->kset.kobj,&a->attr);
 		subsys_put(s);