audit: clean up refcounting in audit-tree

Drop the initial reference by fsnotify_init_mark early instead of
audit_tree_freeing_mark() at destroy time.

In the cases we destroy the mark before we drop the initial reference we need to
get rid of the get_mark that balances the put_mark in audit_tree_freeing_mark().
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

kernel/audit_tree.c

@@ -292,6 +292,7 @@ static void untag_chunk(struct node *p)
 	spin_unlock(&hash_lock);
 	spin_unlock(&entry->lock);
 	fsnotify_destroy_mark(entry);
+	fsnotify_put_mark(&new->mark);	/* drop initial reference */
 	goto out;
 
 Fallback:
@@ -330,7 +331,6 @@ static int create_chunk(struct inode *inode, struct audit_tree *tree)
 		spin_unlock(&hash_lock);
 		chunk->dead = 1;
 		spin_unlock(&entry->lock);
-		fsnotify_get_mark(entry);
 		fsnotify_destroy_mark(entry);
 		fsnotify_put_mark(entry);
 		return 0;
@@ -346,6 +346,7 @@ static int create_chunk(struct inode *inode, struct audit_tree *tree)
 	insert_hash(chunk);
 	spin_unlock(&hash_lock);
 	spin_unlock(&entry->lock);
+	fsnotify_put_mark(entry);	/* drop initial reference */
 	return 0;
 }
 
@@ -411,7 +412,6 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
 		spin_unlock(&chunk_entry->lock);
 		spin_unlock(&old_entry->lock);
 
-		fsnotify_get_mark(chunk_entry);
 		fsnotify_destroy_mark(chunk_entry);
 
 		fsnotify_put_mark(chunk_entry);
@@ -444,6 +444,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
 	spin_unlock(&chunk_entry->lock);
 	spin_unlock(&old_entry->lock);
 	fsnotify_destroy_mark(old_entry);
+	fsnotify_put_mark(chunk_entry);	/* drop initial reference */
 	fsnotify_put_mark(old_entry); /* pair to fsnotify_find mark_entry */
 	return 0;
 }
@@ -915,7 +916,12 @@ static void audit_tree_freeing_mark(struct fsnotify_mark *entry, struct fsnotify
 	struct audit_chunk *chunk = container_of(entry, struct audit_chunk, mark);
 
 	evict_chunk(chunk);
-	fsnotify_put_mark(entry);
+
+	/*
+	 * We are guaranteed to have at least one reference to the mark from
+	 * either the inode or the caller of fsnotify_destroy_mark().
+	 */
+	BUG_ON(atomic_read(&entry->refcnt) < 1);
 }
 
 static bool audit_tree_send_event(struct fsnotify_group *group, struct inode *inode,