From patchwork Tue Jul 10 06:09:07 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yasuaki Ishimatsu X-Patchwork-Id: 1175961 Return-Path: X-Original-To: patchwork-linux-acpi@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by patchwork2.kernel.org (Postfix) with ESMTP id DE16DDFF34 for ; Tue, 10 Jul 2012 06:09:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753065Ab2GJGJS (ORCPT ); Tue, 10 Jul 2012 02:09:18 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:51984 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752472Ab2GJGJS (ORCPT ); Tue, 10 Jul 2012 02:09:18 -0400 Received: from m4.gw.fujitsu.co.jp (unknown [10.0.50.74]) by fgwmail6.fujitsu.co.jp (Postfix) with ESMTP id CEBFA3EE0BC; Tue, 10 Jul 2012 15:09:16 +0900 (JST) Received: from smail (m4 [127.0.0.1]) by outgoing.m4.gw.fujitsu.co.jp (Postfix) with ESMTP id B27B245DE54; Tue, 10 Jul 2012 15:09:16 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (s4.gw.fujitsu.co.jp [10.0.50.94]) by m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 8EBD845DE50; Tue, 10 Jul 2012 15:09:16 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id 7E5EE1DB8043; Tue, 10 Jul 2012 15:09:16 +0900 (JST) Received: from g01jpexchyt04.g01.fujitsu.local (g01jpexchyt04.g01.fujitsu.local [10.128.194.43]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id 296F01DB803F; Tue, 10 Jul 2012 15:09:16 +0900 (JST) Received: from [127.0.0.1] (10.124.101.33) by g01jpexchyt04.g01.fujitsu.local (10.128.194.43) with Microsoft SMTP Server id 14.2.309.2; Tue, 10 Jul 2012 15:09:12 +0900 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.7.4 Message-ID: <4FFBC703.8010604@jp.fujitsu.com> Date: Tue, 10 Jul 2012 15:09:07 +0900 From: Yasuaki Ishimatsu User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: , , , , Subject: [PATCH v2 2/3] acpi : prevent cpu from becoming online References: <4FFBC66B.7030606@jp.fujitsu.com> In-Reply-To: <4FFBC66B.7030606@jp.fujitsu.com> Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org Even if acpi_processor_handle_eject() offlines cpu, there is a chance to online the cpu after that. So the patch closes the window by using get/put_online_cpus(). Why does the patch change _cpu_up() logic? The patch cares the race of hot-remove cpu and _cpu_up(). If the patch does not change it, there is the following race. hot-remove cpu | _cpu_up() ------------------------------------- ------------------------------------ call acpi_processor_handle_eject() | call cpu_down() | call get_online_cpus() | | call cpu_hotplug_begin() and stop here call arch_unregister_cpu() | call acpi_unmap_lsapic() | call put_online_cpus() | | start and continue _cpu_up() return acpi_processor_remove() | continue hot-remove the cpu | So _cpu_up() can continue to itself. And hot-remove cpu can also continue itself. If the patch changes _cpu_cp() logic, the race disappears as below: hot-remove cpu | _cpu_up() ----------------------------------------------------------------------- call acpi_processor_handle_eject() | call cpu_down() | call get_online_cpus() | | call cpu_hotplug_begin() and stop here call arch_unregister_cpu() | call acpi_unmap_lsapic() | cpu's cpu_present is set | to false by set_cpu_present()| call put_online_cpus() | | start _cpu_up() | check cpu_present() and return -EINVAL return acpi_processor_remove() | continue hot-remove the cpu | Signed-off-by: Yasuaki Ishimatsu --- drivers/acpi/processor_driver.c | 12 ++++++++++++ kernel/cpu.c | 8 +++++--- 2 files changed, 17 insertions(+), 3 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Index: linux-3.5-rc6/drivers/acpi/processor_driver.c =================================================================== --- linux-3.5-rc6.orig/drivers/acpi/processor_driver.c 2012-07-10 13:58:20.862931557 +0900 +++ linux-3.5-rc6/drivers/acpi/processor_driver.c 2012-07-10 14:05:46.318365136 +0900 @@ -850,8 +850,18 @@ static int acpi_processor_handle_eject(s return ret; } + get_online_cpus(); + /* + * Someone might online the cpu again at this point. So we check that + * cpu has been onlined or not. If cpu is online, it returns -EBUSY. + */ + if (unlikely(cpu_online(pr->id))) { + put_online_cpus(); + return -EBUSY; + } arch_unregister_cpu(pr->id); acpi_unmap_lsapic(pr->id); + put_online_cpus(); return ret; } #else Index: linux-3.5-rc6/kernel/cpu.c =================================================================== --- linux-3.5-rc6.orig/kernel/cpu.c 2012-07-08 09:23:56.000000000 +0900 +++ linux-3.5-rc6/kernel/cpu.c 2012-07-10 14:15:26.065113805 +0900 @@ -343,11 +343,14 @@ static int __cpuinit _cpu_up(unsigned in unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0; struct task_struct *idle; - if (cpu_online(cpu) || !cpu_present(cpu)) - return -EINVAL; - cpu_hotplug_begin(); + if (cpu_online(cpu) || !cpu_present(cpu)) { + ret = -EINVAL; + goto out; + } + + idle = idle_thread_get(cpu); if (IS_ERR(idle)) { ret = PTR_ERR(idle);