From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760214Ab0I1A23 (ORCPT ); Mon, 27 Sep 2010 20:28:29 -0400 Received: from mga14.intel.com ([143.182.124.37]:40105 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751502Ab0I1A22 (ORCPT ); Mon, 27 Sep 2010 20:28:28 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.57,244,1283756400"; d="scan'208";a="329395304" Subject: Re: [PATCH -v2 7/7] x86, NMI, Remove do_nmi_callback logic From: Huang Ying To: Don Zickus Cc: Robert Richter , huang ying , Ingo Molnar , "H. Peter Anvin" , "linux-kernel@vger.kernel.org" , Andi Kleen In-Reply-To: <20100927151607.GX26290@redhat.com> References: <1285549026-5008-1-git-send-email-ying.huang@intel.com> <1285549026-5008-7-git-send-email-ying.huang@intel.com> <20100927104426.GD32222@erda.amd.com> <20100927134341.GQ13563@erda.amd.com> <20100927151607.GX26290@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Tue, 28 Sep 2010 08:28:25 +0800 Message-ID: <1285633705.20791.84.camel@yhuang-dev> Mime-Version: 1.0 X-Mailer: Evolution 2.30.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Don, On Mon, 2010-09-27 at 23:16 +0800, Don Zickus wrote: > On Mon, Sep 27, 2010 at 03:43:41PM +0200, Robert Richter wrote: > > On 27.09.10 08:56:44, huang ying wrote: > > > > > >> -static int unknown_nmi_panic_callback(struct pt_regs *regs, int cpu) > > > >> -{ > > > >> - unsigned char reason = get_nmi_reason(); > > > >> - char buf[64]; > > > >> - > > > >> - sprintf(buf, "NMI received for unknown reason %02x\n", reason); > > > >> - die_nmi(buf, regs, 1); /* Always panic here */ > > > >> - return 0; > > > > > > > > You are dropping this code that is different to panic(). > > > > > > What is the difference? Is it relevant? > > > > I think yes, since the code behaves different. Otherwise we could > > remove die_nmi() completly and replace it by panic(). But both are > > different implementions. Maybe we can merge the code, but I didn't > > look at it closly. > > Actually die_nmi is a wrapper around panic with two important pieces. > One, it dumps some registers and two it does another notifier call to > DIE_NMIWATCHDOG (which correlates to another discussion in this patch > series). > > So if we do any consolidation between panic and die_nmi, it should be > convert to die_nmi. But then I wonder if that breaks the original > semantics of 'panic_on_unrecovered_nmi'. I don't think so though. Please take a look at the original code: if (nmi_watchdog_tick(regs, reason)) return; if (!do_nmi_callback(regs, cpu)) #endif /* !CONFIG_LOCKUP_DETECTOR */ unknown_nmi_error(reason, regs); #else unknown_nmi_error(reason, regs); #endif If NMI comes from watchdog, nmi_watchdog_tick() will return 1. So do_nmi_callback() is NOT for watchdog NMI, but for unknown NMI. Why do we call DIE_NMIWATCHDOG for unknown NMI (NOT watchdog NMI)? die_nmi is for watchdog, not unknown NMI. So another issue is registers dumping. If it is necessary, we can dump registers in unknown_nmi_error(). Although I think unknown NMI comes from hardware instead of software, so it does not help much to dump registers. Best Regards, Huang Ying