2.4.20-rc1: oops in drivers/acpi/namespace/nswalk.c (with patch)

I have one machine which has been reliably oopsing in drivers/acpi/namespace/nswalk.c -- this patch makes it work, but I have no idea why. Either way, I thought someone would probably want to look at it.

-hpa

@@ -63,6 +63,8 @@
 
 	FUNCTION_ENTRY ();
 
+	if (!parent_node)
+		return NULL;	/* Uhm... */
 
 	if (!child_node) {
 		/* It's really the parent's _scope_ that we want */