From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752373Ab2E0TMm (ORCPT ); Sun, 27 May 2012 15:12:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:24845 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751848Ab2E0TMi (ORCPT ); Sun, 27 May 2012 15:12:38 -0400 Date: Sun, 27 May 2012 21:11:06 +0200 From: Oleg Nesterov To: "Eric W. Biederman" Cc: Andrew Morton , LKML , Pavel Emelyanov , Cyrill Gorcunov , Louis Rilling , Mike Galbraith Subject: [PATCH v2 -mm 1/1] pidns: find_new_reaper() can no longer switch to init_pid_ns.child_reaper Message-ID: <20120527191106.GC13929@redhat.com> References: <87zk95kper.fsf@xmission.com> <20120521124414.GA20391@redhat.com> <87d35x5ank.fsf_-_@xmission.com> <20120522122315.c3f2118c.akpm@linux-foundation.org> <20120523145239.GA20378@redhat.com> <20120525151526.GA13111@redhat.com> <20120525155941.GA16885@redhat.com> <20120525160008.GB16885@redhat.com> <87pq9sdjhn.fsf@xmission.com> <20120527191032.GB13929@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120527191032.GB13929@redhat.com> 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 find_new_reaper() changes pid_ns->child_reaper, see add0d4df "pid_ns: zap_pid_ns_processes: fix the ->child_reaper changing". The original reason has gone away after the previous patch, ->children list must be empty after zap_pid_ns_processes(). However now we can not switch to init_pid_ns.child_reaper. __unhash_process() relies on the "->child_reaper == parent" check, but this check does not work if the last exiting task is also the child reaper. As Eric sugested, we can change __unhash_process() to use the parent's pid_ns and remove this code. Also, with this change we can move detach_pid(PIDTYPE_PID) back, where it was before the previous fix. Signed-off-by: Oleg Nesterov --- kernel/exit.c | 10 ++-------- 1 files changed, 2 insertions(+), 8 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index 6d66cd2..6424e6b 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -64,6 +64,7 @@ static void exit_mm(struct task_struct * tsk); static void __unhash_process(struct task_struct *p, bool group_dead) { nr_threads--; + detach_pid(p, PIDTYPE_PID); if (group_dead) { detach_pid(p, PIDTYPE_PGID); detach_pid(p, PIDTYPE_SID); @@ -79,13 +80,12 @@ static void __unhash_process(struct task_struct *p, bool group_dead) if (IS_ENABLED(CONFIG_PID_NS)) { struct task_struct *parent = p->real_parent; - if ((task_active_pid_ns(p)->child_reaper == parent) && + if ((task_active_pid_ns(parent)->child_reaper == parent) && list_empty(&parent->children) && (parent->flags & PF_EXITING)) wake_up_process(parent); } } - detach_pid(p, PIDTYPE_PID); list_del_rcu(&p->thread_group); } @@ -732,12 +732,6 @@ static struct task_struct *find_new_reaper(struct task_struct *father) zap_pid_ns_processes(pid_ns); write_lock_irq(&tasklist_lock); - /* - * 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; } else if (father->signal->has_child_subreaper) { struct task_struct *reaper; -- 1.5.5.1