From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751927Ab3AJOXB (ORCPT ); Thu, 10 Jan 2013 09:23:01 -0500 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:43882 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750800Ab3AJOXA (ORCPT ); Thu, 10 Jan 2013 09:23:00 -0500 Date: Thu, 10 Jan 2013 14:22:45 +0000 From: Russell King - ARM Linux To: Don Zickus Cc: Colin Cross , linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , liu chuansheng , Thomas Gleixner , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] hardlockup: detect hard lockups without NMIs using secondary cpus Message-ID: <20130110142245.GE19944@n2100.arm.linux.org.uk> References: <1357783059-13923-1-git-send-email-ccross@android.com> <20130110140215.GP88797@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130110140215.GP88797@redhat.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 10, 2013 at 09:02:15AM -0500, Don Zickus wrote: > On Wed, Jan 09, 2013 at 05:57:39PM -0800, Colin Cross wrote: > > Emulate NMIs on systems where they are not available by using timer > > interrupts on other cpus. Each cpu will use its softlockup hrtimer > > to check that the next cpu is processing hrtimer interrupts by > > verifying that a counter is increasing. > > > > This patch is useful on systems where the hardlockup detector is not > > available due to a lack of NMIs, for example most ARM SoCs. > > I have seen other cpus, like Sparc I think, create a 'virtual NMI' by > reserving an IRQ line as 'special' (can not be masked). Not sure if that > is something worth looking at here (or even possible). No it isn't, because that assumes that things like spin_lock_irqsave() won't mask that interrupt. We don't have the facility to do that.