From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758457Ab2IGHBr (ORCPT ); Fri, 7 Sep 2012 03:01:47 -0400 Received: from casper.infradead.org ([85.118.1.10]:58173 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754463Ab2IGHBp convert rfc822-to-8bit (ORCPT ); Fri, 7 Sep 2012 03:01:45 -0400 Message-ID: <1347001230.18408.72.camel@twins> Subject: Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings From: Peter Zijlstra To: paulmck@linux.vnet.ibm.com Cc: Steven Rostedt , linux-kernel@vger.kernel.org, mingo@elte.hu, 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, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" Date: Fri, 07 Sep 2012 09:00:30 +0200 In-Reply-To: <20120906222239.GQ2448@linux.vnet.ibm.com> References: <20120830185607.GA32148@linux.vnet.ibm.com> <1346352988-32444-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346352988-32444-11-git-send-email-paulmck@linux.vnet.ibm.com> <1346943414.18408.31.camel@twins> <1346944049.1680.23.camel@gandalf.local.home> <1346944758.18408.35.camel@twins> <20120906210354.GC2448@linux.vnet.ibm.com> <1346967661.1680.52.camel@gandalf.local.home> <20120906215838.GM2448@linux.vnet.ibm.com> <1346969153.1680.60.camel@gandalf.local.home> <20120906222239.GQ2448@linux.vnet.ibm.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2012-09-06 at 15:22 -0700, Paul E. McKenney wrote: > Ah! > > It is perfectly legal to avoid -starting- an RCU grace period for a > minute, or even longer. If RCU has nothing to do, in other words, if no > one registers any RCU callbacks, then RCU need not start a grace period. > > Of course, this would mean that it would eventually be a full minute > since the last start of a grace period. This is not a problem, after > all, Linux went through a full ten years before experiencing its first > grace period. > > But the stall-warning code just checked how long it had been since > the last start of a grace period, failing to note that this grace > period had long since completed. So it splatted out a warning. > This warning was spurious in the sense that there was no bug aside > from the missing check that the grace period was still in progress. > > And this commit fixes that bug in RCU. OK, that makes sense.. it just looks like both Steve and me got confused by the initial changelog.