Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754085AbbG2IXi (ORCPT ); Wed, 29 Jul 2015 04:23:38 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:37269 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753570AbbG2IXe (ORCPT ); Wed, 29 Jul 2015 04:23:34 -0400 Date: Wed, 29 Jul 2015 10:23:30 +0200 From: Michal Hocko To: =?utf-8?B?5rKz5ZCI6Iux5a6PIC8gS0FXQUnvvIxISURFSElSTw==?= Cc: Jonathan Corbet , Peter Zijlstra , Ingo Molnar , "Eric W. Biederman" , "H. Peter Anvin" , Andrew Morton , Thomas Gleixner , Vivek Goyal , "linux-doc@vger.kernel.org" , "x86@kernel.org" , "kexec@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Ingo Molnar , =?utf-8?B?5bmz5p2+6ZuF5bezIC8gSElSQU1BVFXvvIxNQVNBTUk=?= Subject: Re: Re: [V2 PATCH 1/3] x86/panic: Fix re-entrance problem due to panic on NMI Message-ID: <20150729082329.GA15801@dhcp22.suse.cz> References: <20150727015850.4928.87717.stgit@softrs> <20150727015850.4928.50289.stgit@softrs> <20150727143405.GF11317@dhcp22.suse.cz> <55B6E2A3.8070004@hitachi.com> <04EAB7311EE43145B2D3536183D1A8445491D5E8@GSjpTKYDCembx31.service.hitachi.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <04EAB7311EE43145B2D3536183D1A8445491D5E8@GSjpTKYDCembx31.service.hitachi.net> 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: 1756 Lines: 44 On Wed 29-07-15 05:48:47, 河合英宏 / KAWAI，HIDEHIRO wrote: > Hi, > > > From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Hidehiro Kawai > > (2015/07/27 23:34), Michal Hocko wrote: > > > On Mon 27-07-15 10:58:50, Hidehiro Kawai wrote: > [...] > > > The check could be also relaxed a bit and nmi_panic would > > > return only if the ongoing panic is the current cpu when we really have > > > to return and allow the preempted panic to finish. > > > > It's reasonable. I'll do that in the next version. > > I noticed atomic_read() is insufficient. Please consider the following > scenario. > > CPU 1: call panic() in the normal context > CPU 0: call nmi_panic(), check the value of panic_cpu, then call panic() > CPU 1: set 1 to panic_cpu > CPU 0: fail to set 0 to panic_cpu, then do an infinite loop > CPU 1: call crash_kexec(), then call kdump_nmi_shootdown_cpus() > > At this point, since CPU 0 loops in NMI context, it never executes > the NMI handler registered by kdump_nmi_shootdown_cpus(). This means > that no register states are saved and no cleanups for VMX/SVM are > performed. Yes this is true but it is no different from the current state, isn't it? So if you want to handle that then it deserves a separate patch. It is certainly not harmful wrt. panic behavior. > So, we should still use atomic_cmpxchg() in nmi_panic() to > prevent other cpus from running panic routines. Not sure what you mean by that. -- 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/