From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751719Ab1GTNZj (ORCPT ); Wed, 20 Jul 2011 09:25:39 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:35129 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751006Ab1GTNZi (ORCPT ); Wed, 20 Jul 2011 09:25:38 -0400 Date: Wed, 20 Jul 2011 06:25:30 -0700 From: "Paul E. McKenney" To: Peter Zijlstra 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, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org, greearb@candelatech.com, edt@aei.ca, "Paul E. McKenney" Subject: Re: [PATCH tip/core/urgent 4/7] rcu: protect __rcu_read_unlock() against scheduler-using irq handlers Message-ID: <20110720132530.GF2400@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110720001738.GA16369@linux.vnet.ibm.com> <1311121103-16978-4-git-send-email-paulmck@linux.vnet.ibm.com> <1311166467.5345.78.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1311166467.5345.78.camel@twins> 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 Wed, Jul 20, 2011 at 02:54:27PM +0200, Peter Zijlstra wrote: > On Tue, 2011-07-19 at 17:18 -0700, Paul E. McKenney wrote: > > @@ -391,10 +400,15 @@ void __rcu_read_unlock(void) > > struct task_struct *t = current; > > > > barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ > > - if (--t->rcu_read_lock_nesting == 0) { > > - barrier(); /* decr before ->rcu_read_unlock_special load */ > > + if (t->rcu_read_lock_nesting != 1) > > + --t->rcu_read_lock_nesting; > > + else { > > + t->rcu_read_lock_nesting = INT_MIN; > > + barrier(); /* assign before ->rcu_read_unlock_special load */ > > if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) > > rcu_read_unlock_special(t); > > + barrier(); /* ->rcu_read_unlock_special load before assign */ > > + t->rcu_read_lock_nesting = 0; > > } > > #ifdef CONFIG_PROVE_LOCKING > > WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0); > > But won't the above change make that WARN_ON_ONCE() invalid? Yes, please see the patch I just sent. So that warning was spurious, and if that was the only problem... Thanx, Paul