[kobject] Remove kobj_lock and use lockless refcounting.

The only thing preventing this from happening earlier was the circular sysfs
registration dependency - it would need to be initialized before it was 
registered, but needed to be registered before it was initialized. 

With kobjects gone from struct filesystem_type, the dependency no longer 
exists and we don't have to special-case the possibility that a kobject will
be passed to kobject_get with a refcount == 0. 

Note that a kobject with a count of 0 in that function is still a bug, but 
one in the subsystem making the call. We should add a debugging hook to dump
the stack if it does happen. 

lib/kobject.c

@@ -17,10 +17,6 @@
 #include <linux/module.h>
 #include <linux/stat.h>
 
-/* This lock can be removed entirely when the sysfs_init() code is cleaned up
- * to not try to reference itself before it is initialized. */
-static spinlock_t kobj_lock = SPIN_LOCK_UNLOCKED;
-
 /**
  *	populate_dir - populate directory with attributes.
  *	@kobj:	object we're working on.
@@ -350,14 +346,11 @@ void kobject_unregister(struct kobject * kobj)
 struct kobject * kobject_get(struct kobject * kobj)
 {
 	struct kobject * ret = kobj;
-	unsigned long flags;
 
-	spin_lock_irqsave(&kobj_lock, flags);
-	if (kobj && atomic_read(&kobj->refcount) > 0)
+	if (kobj)
 		atomic_inc(&kobj->refcount);
 	else
 		ret = NULL;
-	spin_unlock_irqrestore(&kobj_lock, flags);
 	return ret;
 }
 
@@ -387,15 +380,8 @@ void kobject_cleanup(struct kobject * kobj)
 
 void kobject_put(struct kobject * kobj)
 {
-	unsigned long flags;
-
-	local_irq_save(flags);
-	if (atomic_dec_and_lock(&kobj->refcount, &kobj_lock)) {
-		spin_unlock_irqrestore(&kobj_lock, flags);
+	if (atomic_dec_and_test(&kobj->refcount))
 		kobject_cleanup(kobj);
-	} else {
-		local_irq_restore(flags);
-	}
 }