From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932101AbWDFSHM (ORCPT ); Thu, 6 Apr 2006 14:07:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932120AbWDFSHL (ORCPT ); Thu, 6 Apr 2006 14:07:11 -0400 Received: from mail.tv-sign.ru ([213.234.233.51]:64663 "EHLO several.ru") by vger.kernel.org with ESMTP id S932101AbWDFSHK (ORCPT ); Thu, 6 Apr 2006 14:07:10 -0400 Date: Fri, 7 Apr 2006 02:04:03 +0400 From: Oleg Nesterov To: Andrew Morton , "Eric W. Biederman" Cc: linux-kernel@vger.kernel.org Subject: [PATCH rc1-mm] de_thread: fix deadlockable process addition Message-ID: <20060406220403.GA205@oleg> 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 X-Mailing-List: linux-kernel@vger.kernel.org On top of task-make-task-list-manipulations-rcu-safe.patch This patch pidhash-kill-switch_exec_pids.patch changed de_thread() so that it doesn't remove 'leader' from it's thread group. However de_thread() still adds current to init_task.tasks without removing 'leader' from this list. What if another CLONE_VM task starts do_coredump() after de_thread() drops tasklist_lock but before it calls release_task(leader) ? do_coredump()->zap_threads() will find this thread group twice on init_task.tasks list. And it will increment mm->core_waiters twice for the new leader (current in de_thread). So, exit_mm()->complete(mm->core_startup_done) doesn't happen, and we have a deadlock. Signed-off-by: Oleg Nesterov --- MM/fs/exec.c~0_DET 2006-04-06 22:37:33.000000000 +0400 +++ MM/fs/exec.c 2006-04-06 22:51:51.000000000 +0400 @@ -713,7 +713,7 @@ static int de_thread(struct task_struct attach_pid(current, PIDTYPE_PID, current->pid); attach_pid(current, PIDTYPE_PGID, current->signal->pgrp); attach_pid(current, PIDTYPE_SID, current->signal->session); - list_add_tail_rcu(¤t->tasks, &init_task.tasks); + list_replace_rcu(&leader->tasks, ¤t->tasks); current->parent = current->real_parent = leader->real_parent; leader->parent = leader->real_parent = child_reaper; --- MM/kernel/exit.c~0_DET 2006-03-23 23:02:53.000000000 +0300 +++ MM/kernel/exit.c 2006-04-06 23:01:37.000000000 +0400 @@ -55,7 +55,9 @@ static void __unhash_process(struct task detach_pid(p, PIDTYPE_PGID); detach_pid(p, PIDTYPE_SID); - list_del_rcu(&p->tasks); + /* see de_thread()->list_replace_rcu() */ + if (likely(p->tasks.prev != LIST_POISON2)) + list_del_rcu(&p->tasks); __get_cpu_var(process_counts)--; } list_del_rcu(&p->thread_group);