From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752113Ab1IZRfD (ORCPT ); Mon, 26 Sep 2011 13:35:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:23099 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751581Ab1IZRfB (ORCPT ); Mon, 26 Sep 2011 13:35:01 -0400 Date: Mon, 26 Sep 2011 19:06:32 +0200 From: Oleg Nesterov To: Greg KH Cc: Tejun Heo , Luke Macken , stable@kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH stable-3.0] ptrace: don't clear GROUP_STOP_SIGMASK on double-stop Message-ID: <20110926170632.GA16936@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org https://bugzilla.redhat.com/show_bug.cgi?id=740121 1. Luke Macken triggered WARN_ON(!(group_stop & GROUP_STOP_SIGMASK)) in do_signal_stop(). This is because do_signal_stop() clears GROUP_STOP_SIGMASK part unconditionally but doesn't update it if task_is_stopped(). 2. Looking at this problem I noticed that WARN_ON_ONCE(!ptrace) is not right, a stopped-but-resumed tracee can clone the untraced thread in the SIGNAL_STOP_STOPPED group, the new thread can start another group-stop. Remove this warning, we need more fixes to make it true. Reported-by: Luke Macken Signed-off-by: Oleg Nesterov --- 3.0/kernel/signal.c +++ 3.0/kernel/signal.c @@ -1894,21 +1894,19 @@ static int do_signal_stop(int signr) */ if (!(sig->flags & SIGNAL_STOP_STOPPED)) sig->group_exit_code = signr; - else - WARN_ON_ONCE(!task_ptrace(current)); current->group_stop &= ~GROUP_STOP_SIGMASK; current->group_stop |= signr | gstop; sig->group_stop_count = 1; for (t = next_thread(current); t != current; t = next_thread(t)) { - t->group_stop &= ~GROUP_STOP_SIGMASK; /* * Setting state to TASK_STOPPED for a group * stop is always done with the siglock held, * so this check has no races. */ if (!(t->flags & PF_EXITING) && !task_is_stopped(t)) { + t->group_stop &= ~GROUP_STOP_SIGMASK; t->group_stop |= signr | gstop; sig->group_stop_count++; signal_wake_up(t, 0);