linux-kernel - [PATCH 3/3] ptrace_untrace: fix the SIGNAL_STOP

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Message-ID: <20090208184730.GA27086@redhat.com>
Date:	Sun, 8 Feb 2009 19:47:30 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jerome Marchand <jmarchan@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] ptrace_untrace: fix the SIGNAL_STOP_STOPPED check

This bug is ancient too. ptrace_untrace() must not resume the task
if the group stop in progress, we should set TASK_STOPPED instead.

Unfortunately, we still have problems here:

	- if the process/thread was traced, SIGNAL_STOP_STOPPED
	  does not necessary means this thread group is stopped.

	- ptrace breaks the bookkeeping of ->group_stop_count.

(the comment above ptrace_untrace() doesn't look exactly right too).

Signed-off-by: Oleg Nesterov <oleg@...hat.com>

--- 6.29-rc3/kernel/ptrace.c~3_FIX_STOPPED	2009-02-08 06:22:26.000000000 +0100
+++ 6.29-rc3/kernel/ptrace.c	2009-02-08 08:52:14.000000000 +0100
@@ -60,7 +60,8 @@ static void ptrace_untrace(struct task_s
 {
 	spin_lock(&child->sighand->siglock);
 	if (task_is_traced(child)) {
-		if (child->signal->flags & SIGNAL_STOP_STOPPED)
+		if (child->signal->flags & SIGNAL_STOP_STOPPED ||
+		    child->signal->group_stop_count)
 			__set_task_state(child, TASK_STOPPED);
 		else
 			wake_up_process(child);

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