Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752071Ab1CWGfh (ORCPT ); Wed, 23 Mar 2011 02:35:37 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:50546 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750997Ab1CWGff (ORCPT ); Wed, 23 Mar 2011 02:35:35 -0400 Date: Tue, 22 Mar 2011 23:35:24 -0700 From: "Paul E. McKenney" To: Joe Korty Cc: "fweisbec@gmail.com" , "peterz@infradead.org" , "laijs@cn.fujitsu.com" , "mathieu.desnoyers@efficios.com" , "dhowells@redhat.com" , "loic.minier@linaro.org" , "dhaval.giani@gmail.com" , "tglx@linutronix.de" , "josh@joshtriplett.org" , "houston.jim@comcast.net" , "andi@firstfloor.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 8/9] jrcu: fix broken rcu_barrier Message-ID: <20110323063524.GS2322@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110314035044.GA12990@tsunami.ccur.com> <20110314084718.GH2167@linux.vnet.ibm.com> <20110314220928.GA1348@tsunami.ccur.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110314220928.GA1348@tsunami.ccur.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1409 Lines: 35 On Mon, Mar 14, 2011 at 06:09:28PM -0400, Joe Korty wrote: > On Mon, Mar 14, 2011 at 04:47:18AM -0400, Paul E. McKenney wrote: > > On Sun, Mar 13, 2011 at 11:50:44PM -0400, Joe Korty wrote: > > > +void rcu_barrier(void) > > > +{ > > > + synchronize_sched(); > > > + synchronize_sched(); > > > +} > > > > This is still broken. You need to wait until all pre-existing RCU > > callbacks on all CPUs have been invoked. Although this does guarantee > > that all callbacks on the current CPU have been invoked, if one of the > > other CPUs is busy, it might not yet have processed the callbacks from > > earlier grace periods. The usual way to take care of this is to post > > a callback on each CPU, then wait for them all to be invoked. > > Hi Paul, > JRCU (eventually) chains together all callbacks from all > cpus into a single queue and then it expires that single > queue. So the double synchronize_sched() should work as > a rcu_barrier implementation. Hello, Joe, So the following grace period is not permitted to start until all of the callbacks from the prior grace period have been invoked? Or am I missing something subtle here? Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/