From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755578Ab0JTAXS (ORCPT ); Tue, 19 Oct 2010 20:23:18 -0400 Received: from mga02.intel.com ([134.134.136.20]:45660 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754807Ab0JTAXP (ORCPT ); Tue, 19 Oct 2010 20:23:15 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.57,353,1283756400"; d="scan'208";a="565602858" Subject: Re: [PATCH 4/5] x86, NMI: Allow NMI reason io port (0x61) to be processed on any CPU From: Huang Ying To: Don Zickus , Robert Richter Cc: "mingo@elte.hu" , "andi@firstfloor.org" , "linux-kernel@vger.kernel.org" , "peterz@infradead.org" In-Reply-To: <20101019183720.GN4140@redhat.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> Content-Type: text/plain; charset="UTF-8" Date: Wed, 20 Oct 2010 08:23:12 +0800 Message-ID: <1287534192.3026.9.camel@yhuang-dev> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Best Regards, Huang Ying