linux-kernel - [PATCH 2/4] reparent_thread: fix the "is it traced" check

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Message-ID: <20090129080558.GA26871@redhat.com>
Date:	Thu, 29 Jan 2009 09:05:58 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/4] reparent_thread: fix the "is it traced" check

reparent_thread() uses ptrace_reparented() to check whether this thread
is ptraced, in that case we should not notify the new parent.

But ptrace_reparented() is not exactly correct when the reparented thread
is traced by /sbin/init, because forget_original_parent() has already
changed ->real_parent.

Currently, the only problem is the false notification. But with the next
patch the kernel crash in this (yes, pathological) case.

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

--- 6.29-rc3/kernel/exit.c~6_FIX_PTRACE_CHECK	2009-01-29 06:21:51.000000000 +0100
+++ 6.29-rc3/kernel/exit.c	2009-01-29 06:57:09.000000000 +0100
@@ -826,7 +826,7 @@ static void reparent_thread(struct task_
 	/* If we'd notified the old parent about this child's death,
 	 * also notify the new parent.
 	 */
-	if (!ptrace_reparented(p) &&
+	if (!p->ptrace &&
 	    p->exit_state == EXIT_ZOMBIE && thread_group_empty(p))
 		do_notify_parent(p, p->exit_signal);
 

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