[PATCH] O(1) sys_exit(), threading, scalable-exit-2.5.31-A6

This fixes the ptrace wait4() anomaly that can be observed in any
previous Linux kernel i could get my hands at.

If the parent still has other children (that are being traced by
somebody), we wait for them or return immediately without an error in
case of WNOHANG.

kernel/exit.c

@@ -731,7 +731,7 @@ asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options, struc
 		tsk = next_thread(tsk);
 	} while (tsk != current);
 	read_unlock(&tasklist_lock);
-	if (flag) {
+	if (flag || !list_empty(&current->ptrace_children)) {
 		retval = 0;
 		if (options & WNOHANG)
 			goto end_wait4;