Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753029AbbB0NPL (ORCPT ); Fri, 27 Feb 2015 08:15:11 -0500 Received: from mx1.redhat.com ([209.132.183.28]:55538 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752318AbbB0NPJ (ORCPT ); Fri, 27 Feb 2015 08:15:09 -0500 Message-ID: <54F06DC7.9060900@redhat.com> Date: Fri, 27 Feb 2015 08:14:47 -0500 From: Prarit Bhargava User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131028 Thunderbird/17.0.10 MIME-Version: 1.0 To: Naoya Horiguchi CC: Naoya Horiguchi , Tony Luck , Borislav Petkov , Vivek Goyal , "linux-kernel@vger.kernel.org" , Junichi Nomura , Kiyoshi Ueda Subject: Re: [PATCH v2 1/2] x86: mce: kexec: turn off MCE in kexec References: <1425013116-23581-1-git-send-email-n-horiguchi@ah.jp.nec.com> <54F05080.9090605@redhat.com> <54F06718.3020401@gmail.com> In-Reply-To: <54F06718.3020401@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2217 Lines: 51 On 02/27/2015 07:46 AM, Naoya Horiguchi wrote: > Hi Prarit, > > On Fri, Feb 27, 2015 at 06:09:52AM -0500, Prarit Bhargava wrote: > ... >> > @@ -157,6 +160,11 @@ void native_machine_crash_shutdown(struct pt_regs *regs) >> > /* The kernel is broken so disable interrupts */ >> > local_irq_disable(); >> > >> > + /* >> > + * We can't expect MCE handling to work any more, so turn it off. >> > + */ >> > + cpu_emergency_mce_disable(); >> >> What if the system is actually having problems with MCE errors -- which are >> leading to system panics of some sort. Do you *really* want the system to >> continue on at that point? > > Yes, when running the above code, the system doesn't run any business logic, > so no worry about consuming broken data caused by HW errors. > And what we really want to get is any kind of information to find out what > caused the 1st panic, which are likely to be contained in kdump data. > So I think it's justified to improve the success rate of kdump by continuing > the operation here. I looked into it a bit further -- IIUC (according to the Intel spec) disabling MCE this way will result in power cycle of the system if an MCE is detected. So I guess it isn't a worry for Intel. If anyone from AMD can hazard a guess what happens in their case it would be appreciated. I still don't like this approach all that much as a corrected non-fatal error is something I would want to know about as an admin, but that risk is mitigated by BMC and system monitoring hardware. >But the MCE handler is still enabled after that, so >if MCE happens and broadcasts around CPUs after the main thread starts the >2nd kernel (which might not start MCE yet, or might decide not to start MCE,) >MCE handler runs only on the other CPUs (not on the main thread,) leading to >kernel panic with MCE synchronization. Not having looked at the code (and relying on your description) -- there is no way to disable the MCE handler? P. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/