Looks like 2.6.15-rc1-mm1 has total crap in ptrace_get_task_struct
(and it looks like my fault because I sent out a wrong patch).

The patch below should fix it:

Index: linux-2.6/kernel/ptrace.c
===================================================================
--- linux-2.6.orig/kernel/ptrace.c	2005-11-18 10:25:35.000000000 +0100
+++ linux-2.6/kernel/ptrace.c	2005-11-18 10:25:54.000000000 +0100
@@ -459,7 +459,7 @@
 	read_unlock(&tasklist_lock);
 	if (!child)
 		return ERR_PTR(-ESRCH);
-	return 0;
+	return child;
 }
 
 #ifndef __ARCH_SYS_PTRACE