From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753275Ab1G2Xoh (ORCPT ); Fri, 29 Jul 2011 19:44:37 -0400 Received: from smtp-out.google.com ([74.125.121.67]:32400 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753058Ab1G2Xog convert rfc822-to-8bit (ORCPT ); Fri, 29 Jul 2011 19:44:36 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=dkim-signature:mime-version:in-reply-to:references:date: message-id:subject:from:to:cc:content-type: content-transfer-encoding:x-system-of-record; b=WsrJbV7LurJVL7JPyY9ZY2EFKIFvzdA/KxLUGWJ/c+c3pk3AU6TCgSzr4RhSxVATh 6PRuqVrUopX5lp1LK98JA== MIME-Version: 1.0 In-Reply-To: <20110729205538.GD14343@redhat.com> References: <1311271873-10879-1-git-send-email-zakmagnus@google.com> <20110722195340.GF3765@redhat.com> <20110725124451.GA2866@redhat.com> <20110729205538.GD14343@redhat.com> Date: Fri, 29 Jul 2011 16:12:32 -0700 Message-ID: Subject: Re: [PATCH v3 2/2] Make hard lockup detection use timestamps From: ZAK Magnus To: Don Zickus Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Mandeep Singh Baines Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Are you saying that any call to printk() will touch the watchdogs? I wasn't aware of that and it doesn't seem to comply with my observations too well, either. Then again, at the moment I don't understand some of the things I'm currently seeing so I could just be wrong. On Fri, Jul 29, 2011 at 1:55 PM, Don Zickus wrote: > 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 >