From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752738AbYKDMES (ORCPT ); Tue, 4 Nov 2008 07:04:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751392AbYKDMEF (ORCPT ); Tue, 4 Nov 2008 07:04:05 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:60146 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751382AbYKDMEE (ORCPT ); Tue, 4 Nov 2008 07:04:04 -0500 Date: Tue, 4 Nov 2008 13:03:55 +0100 From: Ingo Molnar To: =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker Cc: Steven Rostedt , Linux Kernel Subject: Re: [PATCH] tracing: use raw spinlocks instead of spinlocks Message-ID: <20081104120355.GA19969@elte.hu> References: <490E3F73.1000405@gmail.com> <20081103064647.GA4826@elte.hu> <20081104094341.GO23790@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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,DNS_FROM_SECURITYSAGE autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] 0.0 DNS_FROM_SECURITYSAGE RBL: Envelope sender in blackholes.securitysage.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Frédéric Weisbecker wrote: > 2008/11/4 Ingo Molnar : > > lockdep works via a completely different principle: it instruments all > > the actual lock acquire/release calls and builds a graph of lock > > dependencies in the system, as it happens. > > > > It also guarantees that all the observed locking rules are followed > > (i.e. it proves that as long as you dont get any messages from > > lockdep, all the locking patterns are mathematically safe). > > > > So a lockdep message will most of the time occur much easier than a > > real lockup would occur - as lockdep only needs to observe > > inconsistent locking patterns to prove that a lockup _could_ occur. > > > Ok, so if there is such an error, I could (hopefully) see it with > early_printk.... > > > > The NMI watchdog just observes the system and complains if it sees > > hardirqs not progressing (i.e. a hard lockup). It will detect anything > > that causes a hard lockup. (assuming that the NMI watchdog itself is > > not locked up) > > > > Regarding your lockup ... it's quite hard. Maybe you can get more > > output out of the system by using: > > > > earlyprintk=vga,keep > > > > plus disablig regular tty output. (i.e. not passing any 'console=tty' > > line to the kernel bootup.) > > > > this way you wont get any normal printk activities (which might lock > > up), you should only get the very simple early-printk output. > > > > Good idea. After reading your mail, I had a look on early_printk and > it shoudn't cause any tracing recursion after your patch: the > strings are directly writed to the vga. Great. just make sure normal printk is totally silent. (otherwise you get double lines on the console plus no reduction in recursion risk) i usually add a return; hack to kernel/printk.c:printk(), to make sure it never executes anything. (and add a notrace to it as well) Maybe we could even make this dependent on early_printk=...,keep. Ingo