From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756786AbaEEVnp (ORCPT ); Mon, 5 May 2014 17:43:45 -0400 Received: from g4t3425.houston.hp.com ([15.201.208.53]:60702 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756251AbaEEVno (ORCPT ); Mon, 5 May 2014 17:43:44 -0400 Message-ID: <1399325710.1789.95.camel@misato.fc.hp.com> Subject: Re: [PATCH v5 4/4] x86: initialize secondary CPU only if master CPU will wait for it From: Toshi Kani To: Igor Mammedov Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, bp@suse.de, paul.gortmaker@windriver.com, JBeulich@suse.com, prarit@redhat.com, drjones@redhat.com, riel@redhat.com, gong.chen@linux.intel.com, andi@firstfloor.org, lenb@kernel.org, rjw@rjwysocki.net, linux-acpi@vger.kernel.org Date: Mon, 05 May 2014 15:35:10 -0600 In-Reply-To: <1399322991-19329-5-git-send-email-imammedo@redhat.com> References: <1399322991-19329-1-git-send-email-imammedo@redhat.com> <1399322991-19329-5-git-send-email-imammedo@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.5 (3.8.5-2.fc19) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2014-05-05 at 22:49 +0200, Igor Mammedov wrote: > Hang is observed on virtual machines during CPU hotplug, > especially in big guests with many CPUs. (It reproducible > more often if host is over-committed). > > It happens because master CPU gives up waiting on > secondary CPU and allows it to run wild. As result > AP causes locking or crashing system. For example > as described here: https://lkml.org/lkml/2014/3/6/257 > > If master CPU have sent STARTUP IPI successfully, > and AP signalled to master CPU that it's ready > to start initialization, make master CPU wait > indefinitely till AP is onlined. > To ensure that AP won't ever run wild, make it > wait at early startup till master CPU confirms its > intention to wait for AP. If AP doesn't respond in 10 > seconds, the master CPU will timeout and cancel > AP onlining. > > Signed-off-by: Igor Mammedov Thanks for the update. Acked-by: Toshi Kani -Toshi