From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751784AbdF3IZk (ORCPT ); Fri, 30 Jun 2017 04:25:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39390 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751579AbdF3IZj (ORCPT ); Fri, 30 Jun 2017 04:25:39 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 0D1D65F795 Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=vkuznets@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 0D1D65F795 From: Vitaly Kuznetsov To: x86@kernel.org Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] x86/smpboot: Unbreak CPU0 hotplug References: <20170626163635.28808-1-vkuznets@redhat.com> Date: Fri, 30 Jun 2017 10:25:36 +0200 In-Reply-To: <20170626163635.28808-1-vkuznets@redhat.com> (Vitaly Kuznetsov's message of "Mon, 26 Jun 2017 18:36:35 +0200") Message-ID: <87fuehvq4f.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 30 Jun 2017 08:25:39 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Vitaly Kuznetsov writes: > A hang on CPU0 onlining after a preceding offlining is observed. Trace > shows that CPU0 is stuck in check_tsc_sync_target() waiting for source > CPU to run check_tsc_sync_source() but this never happens. Source CPU, > in its turn, is stuck on synchronize_sched() which is called from > native_cpu_up() -> do_boot_cpu() -> unregister_nmi_handler(). > > Fix the issue by moving unregister_nmi_handler() from do_boot_cpu() to > native_cpu_up() after cpu onlining is done. > > Signed-off-by: Vitaly Kuznetsov > --- > RFC part: I tested the fix on KVM and Xen guests and it works just fine > but CPU0 hotplug is not something I'm really familiar with, I may be > missing some important details. I also skipped code archeology to figure > out when things got broken. Any comments? This can be considered as non-RFC if not :-) -- Vitaly