From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752923Ab1G2Uzu (ORCPT ); Fri, 29 Jul 2011 16:55:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:11413 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752372Ab1G2Uzt (ORCPT ); Fri, 29 Jul 2011 16:55:49 -0400 Date: Fri, 29 Jul 2011 16:55:38 -0400 From: Don Zickus To: ZAK Magnus Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Mandeep Singh Baines Subject: Re: [PATCH v3 2/2] Make hard lockup detection use timestamps Message-ID: <20110729205538.GD14343@redhat.com> References: <1311271873-10879-1-git-send-email-zakmagnus@google.com> <20110722195340.GF3765@redhat.com> <20110725124451.GA2866@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 28, 2011 at 05:16:00PM -0700, ZAK Magnus wrote: > No news? > > I've been testing and looking into issues and I realized dump_stack() > calls touch_nmi_watchdog(). That wrecks what the patch is trying to do > so I'm changing it to save the trace and print it later after the > stall has completed. This would also resolve some other things you > were saying weren't so good. Hopefully the logic is similar enough > that some things you may have learned still apply. So yeah, the acting of printing was resesting the softlockup counter and delaying it forever. In parallel, rcu has its own stall detector that was going off after a minute or two. Once I routed the printk to trace_printk and disabled dump_stack, everything started working as expected. Now the question is how to avoid shooting ourselves in the foot by printk'ing a message without resetting the hard/soft lock watchdogs. I'll have to think about how to do that. If you can come up with any ideas let me know. We almost need a quiet dump_stack that dumps to a buffer instead of the console. But I am not sure that is worth the effort. Hmm. Cheers, Don