Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752469AbbGWLZr (ORCPT ); Thu, 23 Jul 2015 07:25:47 -0400 Received: from mail-wi0-f182.google.com ([209.85.212.182]:36373 "EHLO mail-wi0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751824AbbGWLZh (ORCPT ); Thu, 23 Jul 2015 07:25:37 -0400 Date: Thu, 23 Jul 2015 13:25:33 +0200 From: Michal Hocko To: Hidehiro Kawai Cc: Jonathan Corbet , Peter Zijlstra , Ingo Molnar , "Eric W. Biederman" , "H. Peter Anvin" , Andrew Morton , Thomas Gleixner , Vivek Goyal , Masami Hiramatsu , x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH 0/3] x86: Fix panic vs. NMI issues Message-ID: <20150723112532.GD9386@dhcp22.suse.cz> References: <20150722021421.5155.74460.stgit@softrs> <20150723082514.GC9386@dhcp22.suse.cz> <55B0BDB7.2050809@hitachi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55B0BDB7.2050809@hitachi.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2359 Lines: 60 On Thu 23-07-15 19:11:03, Hidehiro Kawai wrote: > Hi, > > Thanks for the feedback. > > (2015/07/23 17:25), Michal Hocko wrote: > > Hi, > > > > On Wed 22-07-15 11:14:21, Hidehiro Kawai wrote: > >> When an HA cluster software or administrator detects non-response > >> of a host, they issue an NMI to the host to completely stop current > >> works and take a crash dump. If the kernel has already panicked > >> or is capturing a crash dump at that time, further NMI can cause > >> a crash dump failure. > >> > >> To solve this issue, this patch set does two things: > >> > >> - Don't panic on NMI if the kernel has already panicked > >> - Introduce "noextnmi" boot option which masks external NMI at the > >> boot time (supported only for x86) > > > > I am currently debugging the same issue for our customer. Curiously > > enough the issue happens on a Hitachi HW. > > I found these issues by my white-box testing and source code > reading. So, they haven't happened on our customers yet, but > possibly happen. > > > I haven't posted my patch for an upstream review yet because I still > > do not have a feedback but I believe your solution is unnecessarily > > too complex. Unless I am missing something the following should be enough, > > no? > > Your patch solves some cases, but I think it wouldn't cover > all cases where I want to solve. How about the following cases? > > 1) panic -> acquire panic_lock -> unknown NMI on this CPU -> > panic -> failed to acquire panic_lock -> infinite loop > ==> no one processes kdump procedure. Ohh, I wasn't aware of panic_lock, 93e13a360ba3 ("kdump: fix crash_kexec()/smp_send_stop() race in panic()") has been introduced in 3.3 and I was debugging this on 3.0 based kernel. > 2) crash_kexec w/o entering panic -> acquire kexec_mutex -> > unknown NMI on this CPU -> panic -> crash_kexec -> > failed to acquire kexec_mutex -> return to panic -> smp_send_stop > > Even if with your patch, case 2) causes infinite loop of > try_crash_kexec and no one processes kdump procedure. You are right - I have missed this case. -- Michal Hocko SUSE Labs -- 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/