Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755999Ab1FELgo (ORCPT ); Sun, 5 Jun 2011 07:36:44 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:56140 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755968Ab1FELgm (ORCPT ); Sun, 5 Jun 2011 07:36:42 -0400 Date: Sun, 5 Jun 2011 13:36:27 +0200 From: Ingo Molnar To: Arne Jansen Cc: Peter Zijlstra , Linus Torvalds , mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, efault@gmx.de, npiggin@kernel.dk, akpm@linux-foundation.org, frank.rowand@am.sony.com, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages Message-ID: <20110605113627.GA25724@elte.hu> References: <1307092535.2353.2973.camel@twins> <4DE8B13D.9020302@die-jansens.de> <1307097052.2353.3061.camel@twins> <20110605081747.GA17920@elte.hu> <4DEB4FA7.3050400@die-jansens.de> <20110605095555.GA22058@elte.hu> <4DEB58D8.4000805@die-jansens.de> <20110605110132.GB23463@elte.hu> <20110605111933.GA24592@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110605111933.GA24592@elte.hu> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes 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 Content-Length: 1013 Lines: 38 * Ingo Molnar wrote: > > If the ticks stop this suggests a lockup within the printk code. > > [...] > > In which case the printk-killswitch patch below (to be applied > *instead* of the previous debugging patch i sent) should provide > the desired NMI watchdog output on the serial console. > > Warning: it's entirely untested. Note, since this is an SMP box, if the lockup messages show up with this patch but are mixed up with each other then adding a spinlock around the WARN() would probably help keeping the output serialized. A simple: static DEFINE_SPINLOCK(watchdog_output_lock); ... spin_lock(&watchdog_output_lock); ... [ the WARN_ON() logic. ] ... spin_unlock(&watchdog_output_lock); ... would suffice. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/