From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755373Ab0KHSF3 (ORCPT ); Mon, 8 Nov 2010 13:05:29 -0500 Received: from mail-ew0-f46.google.com ([209.85.215.46]:33963 "EHLO mail-ew0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755278Ab0KHSF2 (ORCPT ); Mon, 8 Nov 2010 13:05:28 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=OIfuPxBBLltShuYt0b4vVYTB21ZFolQdgIXdlrffkUTUi6560k1XpPZgQaitcs4C4Q ujPpOOXAMA83MaNO6IB4LwzV5S13BKb06GTbt2LPyuI5leFE0lFG+hncV1nGqMwpt/CP dNP/RHRiC+7r/FshnC24ej3BRXWSYJ+OTlfho= Date: Mon, 8 Nov 2010 19:05:23 +0100 From: Frederic Weisbecker To: Don Zickus Cc: Peter Zijlstra , Ingo Molnar , LKML , akpm@linux-foundation.org, sergey.senozhatsky@gmail.com Subject: Re: [PATCH v2] watchdog: touch_nmi_watchdog should only touch local cpu not every one Message-ID: <20101108180518.GA5375@nowhere> References: <1289234675-2400-1-git-send-email-dzickus@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1289234675-2400-1-git-send-email-dzickus@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 08, 2010 at 11:44:35AM -0500, Don Zickus wrote: > I ran into a scenario where while one cpu was stuck and should have panic'd > because of the NMI watchdog, it didn't. The reason was another cpu was spewing > stack dumps on to the console. Upon investigation, I noticed that when writing > to the console and also when dumping the stack, the watchdog is touched. > > This causes all the cpus to reset their NMI watchdog flags and the 'stuck' cpu > just spins forever. > > This change causes the semantics of touch_nmi_watchdog to be changed slightly. > Previously, I accidentally changed the semantics and we noticed there was a > codepath in which touch_nmi_watchdog could be touched from a preemtible area. > That caused a BUG() to happen when CONFIG_DEBUG_PREEMPT was enabled. I believe > it was the acpi code. > > My attempt here re-introduces the change to have the touch_nmi_watchdog() code > only touch the local cpu instead of all of the cpus. But instead of using > __get_cpu_var(), I use the __raw_get_cpu_var() version. > > This avoids the preemption problem. However my reasoning wasn't because I was > trying to be lazy. Instead I rationalized it as, well if preemption is enabled > then interrupts should be enabled to and the NMI watchdog will have no reason > to trigger. So it won't matter if the wrong cpu is touched because the percpu > interrupt counters the NMI watchdog uses should still be incrementing. > > V2: remove touch_all_nmi_watchdog code Are you sure you did? :) > +void touch_all_nmi_watchdogs(void) > +{ > if (watchdog_enabled) { > unsigned cpu; > > @@ -151,7 +166,7 @@ void touch_nmi_watchdog(void) > } > touch_softlockup_watchdog(); > } > -EXPORT_SYMBOL(touch_nmi_watchdog); > +EXPORT_SYMBOL(touch_all_nmi_watchdogs); > > #endif > > -- > 1.7.2.3 >