From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933138AbdBVSur (ORCPT ); Wed, 22 Feb 2017 13:50:47 -0500 Received: from mga05.intel.com ([192.55.52.43]:52540 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754917AbdBVSub (ORCPT ); Wed, 22 Feb 2017 13:50:31 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.35,195,1484035200"; d="scan'208";a="61204232" Date: Wed, 22 Feb 2017 10:50:16 -0800 From: "Luck, Tony" To: Xunlei Pang Cc: x86@kernel.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, Borislav Petkov , Ingo Molnar , Dave Young , Prarit Bhargava , Junichi Nomura , Kiyoshi Ueda , Naoya Horiguchi Subject: Re: [PATCH v3] x86/mce: Don't participate in rendezvous process once nmi_shootdown_cpus() was made Message-ID: <20170222185015.GA6141@intel.com> References: <1487736674-2058-1-git-send-email-xlpang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1487736674-2058-1-git-send-email-xlpang@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 22, 2017 at 12:11:14PM +0800, Xunlei Pang wrote: > + /* > + * Cases to bail out to avoid rendezvous process timeout: > + * 1)If this CPU is offline. > + * 2)If crashing_cpu was set, e.g. entering kdump, > + * we need to skip cpus remaining in 1st kernel. > + */ > + if (cpu_is_offline(cpu) || > + (crashing_cpu != -1 && crashing_cpu != cpu)) { > u64 mcgstatus; > > mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS); I think we should document the remaining race conditions. I don't think there is any good way to eliminate them, and they are already pretty small windows. I think the sequence of events looks like: 1 Panic occurs 2 nmi_shootdown_cpus() sets crashing_cpu 3 send NMI to everyone else 4 wait up to a second for other CPUs to take NMI 5 go to kexec code 6 start new kernel 7 new kernel establishes #MC handler If one of the other cpus triggers a machine check while getting to, or in, the NMI handler ... then that cpu will skip processing (if RIPV is set). Between '2' and '5' if crashing_cpu gets a machine check it will execute in the old kernel handler, and do the right thing. There's a fuzzy area between '6' and '7' where a machine check might not end up in the right code. >>From '7' onwards the kexec kernel will handle and machine checks caused by kdump. -Tony