From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758230Ab1GKRAX (ORCPT ); Mon, 11 Jul 2011 13:00:23 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:35052 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758207Ab1GKRAW (ORCPT ); Mon, 11 Jul 2011 13:00:22 -0400 Date: Mon, 11 Jul 2011 10:00:14 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: 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, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org Subject: Re: [PATCH tip/core/rcu 0/6] Check for use of RCU from dyntick-idle mode Message-ID: <20110711170014.GI2245@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110708154331.GA20161@linux.vnet.ibm.com> <20110711160330.GC4109@somewhere.redhat.com> <20110711163848.GF2245@linux.vnet.ibm.com> <20110711164405.GE4109@somewhere.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110711164405.GE4109@somewhere.redhat.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 On Mon, Jul 11, 2011 at 06:44:08PM +0200, Frederic Weisbecker wrote: > On Mon, Jul 11, 2011 at 09:38:48AM -0700, Paul E. McKenney wrote: > > On Mon, Jul 11, 2011 at 06:03:32PM +0200, Frederic Weisbecker wrote: > > > On Fri, Jul 08, 2011 at 08:43:31AM -0700, Paul E. McKenney wrote: > > > > Hello! > > > > > > > > This set of patches adds checks for use of RCU from "extended quiescent > > > > states" such as dyntick-idle mode. Such use is grossly illegal because > > > > RCU by definition ignores CPUs that are in extended quiescent states. > > > > In the case of dyntick-idle mode, the only way for RCU to avoid ignoring > > > > such CPUs would be to wake them up periodically, which would defeat the > > > > whole purpose of dyntick-idle mode. > > > > > > > > The good news is that Frederic got this effort started. The bad news is > > > > that there are several cases where RCU read-side critical sections appear > > > > in dyntick-idle mode. > > > > > > Ok, let me send to you the patch that splits up rcu/tickless logic and I'll try > > > to fix up what you reported to me in ppc. > > > > Very good, thank you! > > > > > BTW, are you aware of other cases? You mentioned "several" :) > > > > PowerPC's hypercall-exit trace event will also cause this complaint. > > Ok looking at this. Oh, and I removed some of my RCU dyntick-idle trace events because they triggered this warning. This would of course be a problem regardless of where the RCU dyntick-idle APIs were called from, so I just took the approach of more carefully placing the trace events. > > Plus I thought you saw some others. > > Nope, mine were spurious. In my v1 rcu_dereference_check warned if rcu read lock > wasn't held but didn't handle the rest of the conditional (another lock held or > simply 1 in rcu_dereference_raw()). > > In the v3, the one you applied, they legitimately disappeared. OK, good to know! Thanx, Paul