Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756269AbYHXPqH (ORCPT ); Sun, 24 Aug 2008 11:46:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751810AbYHXPpY (ORCPT ); Sun, 24 Aug 2008 11:45:24 -0400 Received: from x346.tv-sign.ru ([89.108.83.215]:60260 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751589AbYHXPpW (ORCPT ); Sun, 24 Aug 2008 11:45:22 -0400 Date: Sun, 24 Aug 2008 19:49:11 +0400 From: Oleg Nesterov To: Andrew Morton Cc: "Eric W. Biederman" , Pavel Emelyanov , Robert Rex , Roland McGrath , Serge Hallyn , Sukadev Bhattiprolu , linux-kernel@vger.kernel.org Subject: [PATCH 1/4] pid_ns: zap_pid_ns_processes: fix the ->child_reaper changing Message-ID: <20080824154911.GA3777@tv-sign.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1953 Lines: 46 zap_pid_ns_processes() sets pid_ns->child_reaper = NULL, this is wrong. Yes, we have already killed all tasks in this namespace, and sys_wait4() doesn't see any child. But this doesn't mean ->children list is empty, we may have EXIT_DEAD tasks which are not visible to do_wait(). In that case the subsequent forget_original_parent() will crash the kernel because it will try to re-parent these tasks to the NULL reaper. Even if there are no childs, it is not good that forget_original_parent() uses reaper == NULL. Change the code to set ->child_reaper = init_pid_ns.child_reaper instead. We could use pid_ns->parent->child_reaper as well, I think this does not really matter. These EXIT_DEAD tasks are not visible to the new ->parent after re-parenting, they will silently do release_task() eventually. Note that we must change ->child_reaper, otherwise forget_original_parent() will use reaper == father, and in that case we will hit the (correct) BUG_ON(!list_empty(&father->children)). Signed-off-by: Oleg Nesterov --- 2.6.27-rc4/kernel/pid_namespace.c~1_ZAP_DONT_CLEAR_REAPER 2008-07-30 13:12:49.000000000 +0400 +++ 2.6.27-rc4/kernel/pid_namespace.c 2008-08-24 17:22:59.000000000 +0400 @@ -179,9 +179,12 @@ void zap_pid_ns_processes(struct pid_nam rc = sys_wait4(-1, NULL, __WALL, NULL); } while (rc != -ECHILD); - - /* Child reaper for the pid namespace is going away */ - pid_ns->child_reaper = NULL; + /* + * We can not clear ->child_reaper or leave it alone. + * There may by stealth EXIT_DEAD tasks on ->children, + * forget_original_parent() must move them somewhere. + */ + pid_ns->child_reaper = init_pid_ns.child_reaper; acct_exit_ns(pid_ns); return; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/