From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756472AbZFGVEB (ORCPT ); Sun, 7 Jun 2009 17:04:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755780AbZFGVDh (ORCPT ); Sun, 7 Jun 2009 17:03:37 -0400 Received: from mail-fx0-f213.google.com ([209.85.220.213]:46303 "EHLO mail-fx0-f213.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756133AbZFGVDg (ORCPT ); Sun, 7 Jun 2009 17:03:36 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:content-transfer-encoding :in-reply-to:user-agent; b=YFVDGj6Rd210d446/gRFiFDxLs+MCblLmwr7PWwPcVYtxRcpRF7Fpm3+Ia+vBWKkqk 7F4EaE+UlH/c5gwxRs7iHgT8CAVxYhgoNgPRr92ZbVDd9YEga6YKDBhXoP9V8QUDxPPs OQPdxtqQB1kZHnpgLRETdsZ9nMVC5rQzQg+g4= Date: Mon, 8 Jun 2009 01:03:37 +0400 From: Cyrill Gorcunov To: Yinghai Lu Cc: Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] x86: fix dummy apic read/write warning Message-ID: <20090607210337.GG4547@lenovo> References: <20090606073737.GA3163@elte.hu> <4A2AEAC6.8060404@kernel.org> <20090607070136.GA4547@lenovo> <86802c440906071228x489c3f79q2e1a49dc997e874@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <86802c440906071228x489c3f79q2e1a49dc997e874@mail.gmail.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 [Yinghai Lu - Sun, Jun 07, 2009 at 12:28:07PM -0700] | On Sun, Jun 7, 2009 at 12:01 AM, Cyrill Gorcunov wrote: | > [Yinghai Lu - Sat, Jun 06, 2009 at 03:16:38PM -0700] | > | ingo got | > | [    0.000000] Using APIC driver default | > | [    0.000000] SMP: Allowing 1 CPUs, 0 hotplug CPUs | > | [    0.000000] Local APIC disabled by BIOS -- you can enable it with "lapic" | > | [    0.000000] APIC: disable apic facility | > | [    0.000000] ------------[ cut here ]------------ | > | [    0.000000] WARNING: at arch/x86/kernel/apic/apic.c:254 native_apic_read_dummy+0x2d/0x3b() | > | [    0.000000] Hardware name: HP OmniBook PC | > | | > | we have wrong check in dummy read and write. | > | [we only test on system that have APIC with "disableapic"...] | > | | > | Signed-off-by: yinghai Lu | > | | > | --- | > |  arch/x86/kernel/apic/apic.c |    4 ++-- | > |  1 file changed, 2 insertions(+), 2 deletions(-) | > | | > | Index: linux-2.6/arch/x86/kernel/apic/apic.c | > | =================================================================== | > | --- linux-2.6.orig/arch/x86/kernel/apic/apic.c | > | +++ linux-2.6/arch/x86/kernel/apic/apic.c | > | @@ -246,12 +246,12 @@ static int modern_apic(void) | > |   */ | > |  static void native_apic_write_dummy(u32 reg, u32 v) | > |  { | > | -     WARN_ON_ONCE((cpu_has_apic || !disable_apic)); | > | +     WARN_ON_ONCE((cpu_has_apic && !disable_apic)); | > |  } | > | | > |  static u32 native_apic_read_dummy(u32 reg) | > |  { | > | -     WARN_ON_ONCE((cpu_has_apic || !disable_apic)); | > | +     WARN_ON_ONCE((cpu_has_apic && !disable_apic)); | > |       return 0; | > |  } | > | | > | | > | > No Yinghai, this is wrong. native_apic_write_dummy is not | > admissible to be called after apic->write has been NOP'ified. | > | > If a site calls for apic->write after apic_disable() it's | > a plain *bug* in caller. So we should continute warning if | > cpu_has_apic _or_ !disable_apic. | | ok, just change it to | | WARN_ON_ONCE(1); | | there. There was some scenario where we had legitime apic->write on SMP kernel when cpu goes to halt. Will recheck tomorrow. That is why we added conditional WARN to eliminate uglifying by additional checks (ie we know that apic->write happens but it's nothing serious). Thanks Yinghai! | | > | > Though since for SMP compiled kernel we still rely on | > apic->read the snippet is to be changed to (cpu_has_apic && !disable_apic) | > indeed. | | YH | -- Cyrill