From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752641AbXEaNd5 (ORCPT ); Thu, 31 May 2007 09:33:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751800AbXEaNdu (ORCPT ); Thu, 31 May 2007 09:33:50 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:50221 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751664AbXEaNdt (ORCPT ); Thu, 31 May 2007 09:33:49 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Andrew Morton Cc: Andi Kleen , , Neil Brown , "Rafael J. Wysocki" , Ingo Molnar , Zwane Mwaikambo Subject: [PATCH] x86: Document the hotplug code is incompatible with x86 irq handling Date: Thu, 31 May 2007 07:32:05 -0600 Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org I just realized that except for doing the code review and noticing that the current cpu hotplug code is fundamentally incompatible with x86 I haven't done anything about it. So here is my patch to document what is wrong. The current cpu hotplug code requires irqs to be migrated from a cpu outside of irq context. On x86 ioapics simply do not support this, making the code unfixable without major redesign of the generic cpu hotplug code. So this patch makes CPU_HOTPLUG on x86 depend on CONFIG_BROKEN and adds a WARN_ON so people that do enable it are not in doubt about which part of the code is broken, even if it does work for them. Signed-off-by: Eric W. Biederman --- arch/i386/Kconfig | 2 +- arch/i386/kernel/irq.c | 13 +++++++++++++ arch/x86_64/Kconfig | 2 +- arch/x86_64/kernel/irq.c | 13 +++++++++++++ 4 files changed, 28 insertions(+), 2 deletions(-) diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig index 8770a5d..74444c1 100644 --- a/arch/i386/Kconfig +++ b/arch/i386/Kconfig @@ -892,7 +892,7 @@ config PHYSICAL_ALIGN config HOTPLUG_CPU bool "Support for suspend on SMP and hot-pluggable CPUs (EXPERIMENTAL)" - depends on SMP && HOTPLUG && EXPERIMENTAL && !X86_VOYAGER + depends on SMP && HOTPLUG && EXPERIMENTAL && !X86_VOYAGER && BROKEN ---help--- Say Y here to experiment with turning CPUs off and on, and to enable suspend on SMP systems. CPUs can be controlled through diff --git a/arch/i386/kernel/irq.c b/arch/i386/kernel/irq.c index d2daf67..42aeccb 100644 --- a/arch/i386/kernel/irq.c +++ b/arch/i386/kernel/irq.c @@ -312,6 +312,19 @@ void fixup_irqs(cpumask_t map) unsigned int irq; static int warned; + /* + * Function is so wrong at so many levels. + * - We migrate irqs that are directed at the cpu we are + * removing. + * - We cannot safely migrate ioapic irqs on x86 except in + * side of irq context. + * - We are enabling irqs when the interface requires irqs to + * be disabled. + * Since someone probably finds this useful just warn very + * loudly until cpu hotplug is redesigned. + */ + WARN_ON(1); + for (irq = 0; irq < NR_IRQS; irq++) { cpumask_t mask; if (irq == 2) diff --git a/arch/x86_64/Kconfig b/arch/x86_64/Kconfig index 5ce9443..a61c4f2 100644 --- a/arch/x86_64/Kconfig +++ b/arch/x86_64/Kconfig @@ -429,7 +429,7 @@ config NR_CPUS config HOTPLUG_CPU bool "Support for suspend on SMP and hot-pluggable CPUs (EXPERIMENTAL)" - depends on SMP && HOTPLUG && EXPERIMENTAL + depends on SMP && HOTPLUG && EXPERIMENTAL && BROKEN help Say Y here to experiment with turning CPUs off and on. CPUs can be controlled through /sys/devices/system/cpu/cpu#. diff --git a/arch/x86_64/kernel/irq.c b/arch/x86_64/kernel/irq.c index 3eaceac..da6f282 100644 --- a/arch/x86_64/kernel/irq.c +++ b/arch/x86_64/kernel/irq.c @@ -142,6 +142,19 @@ void fixup_irqs(cpumask_t map) unsigned int irq; static int warned; + /* + * Function is so wrong at so many levels. + * - We migrate irqs that are directed at the cpu we are + * removing. + * - We cannot safely migrate ioapic irqs on x86 except in + * side of irq context. + * - We are enabling irqs when the interface requires irqs to + * be disabled. + * Since someone probably finds this useful just warn very + * loudly until cpu hotplug is redesigned. + */ + WARN_ON(1); + for (irq = 0; irq < NR_IRQS; irq++) { cpumask_t mask; if (irq == 2) -- 1.5.1.1.181.g2de0