From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752200Ab1GTT7P (ORCPT ); Wed, 20 Jul 2011 15:59:15 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:51581 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751368Ab1GTT7O (ORCPT ); Wed, 20 Jul 2011 15:59:14 -0400 Date: Wed, 20 Jul 2011 21:57:42 +0200 From: Ingo Molnar To: "Paul E. McKenney" Cc: Linus Torvalds , Peter Zijlstra , Ben Greear , Ed Tomlinson , linux-kernel@vger.kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org, edward.tomlinson@aero.bombardier.com Subject: Re: [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck Message-ID: <20110720195742.GA14671@elte.hu> References: <20110720044435.GB2400@linux.vnet.ibm.com> <20110720133443.GG2400@linux.vnet.ibm.com> <4E270A0E.6090902@candelatech.com> <20110720171532.GB2313@linux.vnet.ibm.com> <20110720184413.GD17977@elte.hu> <1311187978.29152.58.camel@twins> <20110720192949.GM2313@linux.vnet.ibm.com> <20110720193925.GB7910@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110720193925.GB7910@elte.hu> User-Agent: Mutt/1.5.21 (2010-09-15) 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 * Ingo Molnar wrote: > > * Paul E. McKenney wrote: > > > If my guess is correct, then the minimal non-RCU_BOOST fix is #4 > > (which drags along #3) and #6. Which are not one-liners, but > > somewhat smaller: > > > > b/kernel/rcutree_plugin.h | 12 ++++++------ > > b/kernel/softirq.c | 12 ++++++++++-- > > kernel/rcutree_plugin.h | 31 +++++++++++++++++++++++++------ > > 3 files changed, 41 insertions(+), 14 deletions(-) > > That's half the patch size and half the patch count. > > PeterZ's question is relevant: since we apparently had similar bugs > in v2.6.39 as well, what changed in v3.0 that makes them so urgent > to fix? > > If it's just better instrumentation that proves them better then > i'd suggest fixing this in v3.1 and not risking v3.0 with an > unintended side effect. Ok, i looked some more at the background and the symptoms that people are seeing: kernel crashes and lockups. I think we want these problems fixed in v3.0, even if it was the recent introduction of RCU_BOOST that made it really prominent. Having put some testing into your rcu/urgent branch today i'd feel more comfortable with taking this plus perhaps an RCU_BOOST disabling patch. That makes it all fundamentally tested by a number of people (including those who reported/reproduced the problems). Linus, would that approach be fine with you? I'll send an RFC pull request for the 6 patches as a reply to this mail, in a couple of minutes. Thanks, Ingo