From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933364Ab2IGOmQ (ORCPT ); Fri, 7 Sep 2012 10:42:16 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:14087 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753461Ab2IGOmL (ORCPT ); Fri, 7 Sep 2012 10:42:11 -0400 X-Authority-Analysis: v=2.0 cv=Vb91zSV9 c=1 sm=0 a=rXTBtCOcEpjy1lPqhTCpEQ==:17 a=mNMOxpOpBa8A:10 a=dv6za2K3W50A:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=meVymXHHAAAA:8 a=hUPM8fjf3YcA:10 a=IPOSIB3mYOGryxCwkksA:9 a=PUjeQqilurYA:10 a=rXTBtCOcEpjy1lPqhTCpEQ==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.115.198 Message-ID: <1347028929.8178.8.camel@gandalf.local.home> Subject: Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings From: Steven Rostedt To: Peter Zijlstra Cc: paulmck@linux.vnet.ibm.com, 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 10:42:09 -0400 In-Reply-To: <1347001230.18408.72.camel@twins> 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> <1347001230.18408.72.camel@twins> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.4.3-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2012-09-07 at 09:00 +0200, Peter Zijlstra wrote: > 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. Right, I think the change log needs to be fixed ;-) -- Steve