[PATCH 1/3] ptrace: give more respect to SIGKILL

[Oleg Nesterov <oleg@tv-sign.ru>]

ptrace_stop() has some complicated checks to prevent the scheduling in the
TASK_TRACED state with the pending SIGKILL, but these checks are racy, and
they depend on arch_ptrace_stop_needed().

This patch assumes that the traced task should die asap if it was killed by
SIGKILL, in that case schedule()->signal_pending_state() has no reason to
ignore the TASK_WAKEKILL part of TASK_TRACED, and we can kill this nasty
special case.

Note: do_exit()->ptrace_notify() is special, the killed task can already
dequeue SIGKILL at this point. Another indication that fatal_signal_pending()
is not exactly right.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 26-rc2/include/linux/sched.h~1_KILL_TRACED_CHECK	2008-06-01 16:44:39.000000000 +0400
+++ 26-rc2/include/linux/sched.h	2008-06-01 16:44:39.000000000 +0400
@@ -2034,9 +2034,6 @@ static inline int signal_pending_state(l
 	if (!signal_pending(p))
 		return 0;
 
-	if (state & (__TASK_STOPPED | __TASK_TRACED))
-		return 0;
-
 	return (state & TASK_INTERRUPTIBLE) || __fatal_signal_pending(p);
 }