From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756319Ab0EJTxT (ORCPT ); Mon, 10 May 2010 15:53:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46754 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750990Ab0EJTxK (ORCPT ); Mon, 10 May 2010 15:53:10 -0400 Date: Mon, 10 May 2010 21:50:14 +0200 From: Oleg Nesterov To: Andrew Morton Cc: Cedric Le Goater , Dave Hansen , Eric Biederman , Herbert Poetzl , Ingo Molnar , Mathias Krause , Roland McGrath , Serge Hallyn , Sukadev Bhattiprolu , linux-kernel@vger.kernel.org Subject: [PATCH 2/4] pids: init_struct_pid.tasks should never see the swapper process Message-ID: <20100510195014.GC5249@redhat.com> References: <4BE01C86.3050908@secunet.com> <20100509184510.GA15219@redhat.com> <4BE7B3BD.70901@secunet.com> <20100510194917.GA5249@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100510194917.GA5249@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 "statically initialize struct pid for swapper" commit 820e45db says: Statically initialize a struct pid for the swapper process (pid_t == 0) and attach it to init_task. This is needed so task_pid(), task_pgrp() and task_session() interfaces work on the swapper process also. OK, but: - it doesn't make sense to add init_task.pids[].node into init_struct_pid.tasks[], and in fact this just wrong. idle threads are special, they shouldn't be visible on any global list. In particular do_each_pid_task(init_struct_pid) shouldn't see swapper. This is the actual reason why kill(0, SIGKILL) from /sbin/init (which starts with 0,0 special pids) crashes the kernel. The signal sent to pgid/sid == 0 must never see idle threads, even if the previous patch fixed the crash itself. - we have other idle threads running on the non-boot CPUs, see the next patch. Change INIT_STRUCT_PID/INIT_PID_LINK to create the empty/unhashed hlist_head/hlist_node. Like any other idle thread swapper can never exit, so detach_pid()->__hlist_del() is not possible, but we could change INIT_PID_LINK() to set pprev = &next if needed. All we need is the valid swapper->pids[].pid == &init_struct_pid. Reported-by: Mathias Krause Signed-off-by: Oleg Nesterov --- include/linux/init_task.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- 34-rc1/include/linux/init_task.h~2_INIT_PID_DONT_LINK_SWAPPER 2010-05-10 19:45:27.000000000 +0200 +++ 34-rc1/include/linux/init_task.h 2010-05-10 20:26:08.000000000 +0200 @@ -53,9 +53,9 @@ extern struct group_info init_groups; #define INIT_STRUCT_PID { \ .count = ATOMIC_INIT(1), \ .tasks = { \ - { .first = &init_task.pids[PIDTYPE_PID].node }, \ - { .first = &init_task.pids[PIDTYPE_PGID].node }, \ - { .first = &init_task.pids[PIDTYPE_SID].node }, \ + { .first = NULL }, \ + { .first = NULL }, \ + { .first = NULL }, \ }, \ .rcu = RCU_HEAD_INIT, \ .level = 0, \ @@ -70,7 +70,7 @@ extern struct group_info init_groups; { \ .node = { \ .next = NULL, \ - .pprev = &init_struct_pid.tasks[type].first, \ + .pprev = NULL, \ }, \ .pid = &init_struct_pid, \ }