From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752765Ab0JTKDf (ORCPT ); Wed, 20 Oct 2010 06:03:35 -0400 Received: from am1ehsobe003.messaging.microsoft.com ([213.199.154.206]:23395 "EHLO AM1EHSOBE003.bigfish.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752566Ab0JTKDc (ORCPT ); Wed, 20 Oct 2010 06:03:32 -0400 X-SpamScore: -17 X-BigFish: VPS-17(zzbb2cK936eK1432N98dNzz1202hzz8275bhz32i2a8h43h61h) X-Spam-TCS-SCL: 0:0 X-FB-SS: 0, X-WSS-ID: 0LAL2LF-01-0TV-02 X-M-MSG: Date: Wed, 20 Oct 2010 12:03:16 +0200 From: Robert Richter To: Huang Ying CC: Don Zickus , "mingo@elte.hu" , "andi@firstfloor.org" , "linux-kernel@vger.kernel.org" , "peterz@infradead.org" Subject: Re: [PATCH 4/5] x86, NMI: Allow NMI reason io port (0x61) to be processed on any CPU Message-ID: <20101020100316.GX5969@erda.amd.com> References: <1287195738-3136-1-git-send-email-dzickus@redhat.com> <1287195738-3136-5-git-send-email-dzickus@redhat.com> <20101019150701.GR5969@erda.amd.com> <20101019162507.GU5969@erda.amd.com> <20101019183720.GN4140@redhat.com> <1287534192.3026.9.camel@yhuang-dev> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1287534192.3026.9.camel@yhuang-dev> User-Agent: Mutt/1.5.20 (2009-06-14) X-OriginatorOrg: amd.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19.10.10 20:23:12, Huang Ying wrote: > On Wed, 2010-10-20 at 02:37 +0800, Don Zickus wrote: > > On Tue, Oct 19, 2010 at 06:25:07PM +0200, Robert Richter wrote: > > > On 19.10.10 17:07:01, Robert Richter wrote: > > > > On 15.10.10 22:22:17, Don Zickus wrote: > > > > > From: Huang Ying > > > > > > > > > > In original NMI handler, NMI reason io port (0x61) is only processed > > > > > on BSP. This makes it impossible to hot-remove BSP. To solve the > > > > > issue, a raw spinlock is used to make the port can be processed on any > > > > > CPU. > > > > > > > > > > Signed-off-by: Huang Ying > > > > > Signed-off-by: Don Zickus > > > > > --- > > > > > arch/x86/kernel/traps.c | 45 +++++++++++++++++++++++++-------------------- > > > > > 1 files changed, 25 insertions(+), 20 deletions(-) > > > > > > > > @@ -400,28 +405,28 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs) > > > > > return; > > > > > > > > > > /* Non-CPU-specific NMI: NMI sources can be processed on any CPU */ > > > > > - cpu = smp_processor_id(); > > > > > - /* Only the BSP gets external NMIs from the system. */ > > > > > - if (!cpu) { > > > > > - reason = get_nmi_reason(); > > > > > - if (reason & NMI_REASON_MASK) { > > > > > - if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT) > > > > > - == NOTIFY_STOP) > > > > > - return; > > > > > - if (reason & NMI_REASON_SERR) > > > > > - pci_serr_error(reason, regs); > > > > > - else if (reason & NMI_REASON_IOCHK) > > > > > - io_check_error(reason, regs); > > > > > + raw_spin_lock(&nmi_reason_lock); > > > > > > > > What about using raw_spin_trylock() instead? We don't have to wait > > > > here since we are already processing it by another cpu. > > > > > > This would avoid a global lock and also deadlocking in case of a > > > potential #gp in the nmi handler. > > > > I would feel more comfortable with it too. I can't find a reason where > > trylock would do harm. > > One possible issue can be as follow: > > - PCI SERR NMI raised on CPU 0 > - IOCHK NMI raised on CPU 1 > > If we use try lock, we may get unknown NMI on one CPU. Do you guys think > so? This could be a valid point. On the other side the former implementation to let only handle cpu #0 i/o interrupts didn't trigger unknown nmis, so try_lock wouldn't change much compared to this. To be sure we might do a NOTIFY_STOP in the unknown path if we don't get the lock. -Robert -- Advanced Micro Devices, Inc. Operating System Research Center