From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761577AbYHAVNm (ORCPT ); Fri, 1 Aug 2008 17:13:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760879AbYHAVKF (ORCPT ); Fri, 1 Aug 2008 17:10:05 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:57950 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760877AbYHAVKB (ORCPT ); Fri, 1 Aug 2008 17:10:01 -0400 Date: Fri, 1 Aug 2008 14:09:53 -0700 From: "Paul E. McKenney" To: Ingo Molnar Cc: Linus Torvalds , Alexey Dobriyan , Nick Piggin , "Rafael J. Wysocki" , Kamalesh Babulal , Linux Kernel Mailing List , Adrian Bunk , Andrew Morton , Natalie Protasevich , Kernel Testers List Subject: Re: 2.6.26-rc9-git4: Reported regressions from 2.6.25 Message-ID: <20080801210953.GK14851@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <4yrA-dRoNlD.A.jcB.ny-cIB@albercik> <200807101725.36175.nickpiggin@yahoo.com.au> <20080710110213.GA6688@martell.zuzino.mipt.ru> <20080710173459.GA11648@elte.hu> <20080710180620.GA30844@elte.hu> <20080710204157.GG6877@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080710204157.GG6877@linux.vnet.ibm.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 10, 2008 at 01:41:57PM -0700, Paul E. McKenney wrote: > On Thu, Jul 10, 2008 at 08:06:20PM +0200, Ingo Molnar wrote: > > > > * Ingo Molnar wrote: > > > > > cool! :) > > > > > > (hm, could anyone please resend Nick's original mail? The original one > > > is not in my lkml folder nor on lkml.org - only the quoted one.) > > > > ok, got the mail now now: > > > > | | Annoyed this wasn't a crazy obscure error in the algorithm I could > > | | fix :) [...] > > > > Paul recently ran a formal proof against all sorts of RCU details (and > > found and fixed a few obscure races that way that no-one ever > > triggered), so i'd be quite surprised if we found anything in the core > > algorithm :-) Yeah, it was instead the simple stuff that I messed up... :-/ > > | | [...] I spent all day debugging it and had to make a special test > > | | case (rcutorture didn't seem to trigger it), and a big RCU state > > | | logging infrastructure to log millions of RCU state transitions and > > | | events. Oh well. > > > > nice debugging! > > Indeed!!! > > > Acked-by: Ingo Molnar > > > > i'm wondering why rcutorture didnt trigger it. I do run !HOTPLUG + > > RCU_PREEMPT kernels and never saw this. Nor did Paul. That aspect is > > weird. > > Turns out that my environment was silently re-enabling HOTPLUG_CPU, so I > only -thought- I was testing !CPU_HOTPLUG. Once I forced it to really > disable HOTPLUG_CPU (by manually also specifying CONFIG_SUSPEND=n and > CONFIG_HIBERNATION=n), then rcutorture complained within 10 seconds. > > Sigh!!! And Nick's patch gets rid of the rcutorture failures for me as well, now that I can reproduce them. ;-) Thanx, Paul