From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753973AbYIVR7m (ORCPT ); Mon, 22 Sep 2008 13:59:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752029AbYIVR7e (ORCPT ); Mon, 22 Sep 2008 13:59:34 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:33145 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751985AbYIVR7e (ORCPT ); Mon, 22 Sep 2008 13:59:34 -0400 Date: Mon, 22 Sep 2008 19:59:24 +0200 From: Ingo Molnar To: Aristeu Rozanski Cc: linux-kernel@vger.kernel.org, dzickus@redhat.com, prarit@redhat.com, vgoyal@redhat.com Subject: Re: [PATCH] NMI watchdog: when booting with reset_devices, clear the performance counters Message-ID: <20080922175924.GH10535@elte.hu> References: <20080922171408.GJ16840@redhat.com> <20080922174748.GC10535@elte.hu> <20080922175803.GK16840@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080922175803.GK16840@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Aristeu Rozanski wrote: > > > P4s have a quirk that makes necessary to clear P4_CCCR_OVF bit on the CCCR > > > everytime the PMI is triggered. When booting the kernel with reset_devices > > > (more specific kdump case), the counters reach zero and the PMI will be > > > generated. This is not a problem on other processors but on P4s, it'll > > > continue to generate NMIs until that bit is cleared. Since there may be > > > other users of the performance counters, clear and disable all of them > > > when booting with reset_devices option. > > > > > > We have a P4 box here that crashes because of this problem. Since the kdump > > > kernel usually boots with only one processor active, the second logical > > > unit won't be set up, therefore, MSR_P4_IQ_CCCR1 (and other performance > > > counter registers) won't be cleared and P4_CCCR_OVF may be still set because > > > the previous kernel was using this register. An NMI is triggered because of > > > the MSR_P4_IQ_CCCR1 right after the NMI delivery is enabled, triggering the > > > race fixed on my previous email. > > > > > > Signed-off-by: Aristeu Rozanski > > > Acked-by: Don Zickus > > > Acked-by: Prarit Bhargava > > > Acked-by: Vivek Goyal > > > > applied to tip/x86/nmi-watchdog, thanks. > > > > i'm wondering, is this fix a v2.6.27 candidate? > I believe so. Even being a small affected group (P4 based boxes using NMI > watchdog and kdump), it's fully reproducible. is there a bugzilla.kernel.org entry for it? If not, could you please file it? Thanks, Ingo