From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757931Ab2IDWwL (ORCPT ); Tue, 4 Sep 2012 18:52:11 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:43820 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752333Ab2IDWwH (ORCPT ); Tue, 4 Sep 2012 18:52:07 -0400 Date: Tue, 4 Sep 2012 15:51:53 -0700 From: "Paul E. McKenney" To: Josh Triplett 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, 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, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org Subject: Re: [PATCH tip/core/rcu 10/15] rcu: Protect rcu_node accesses during CPU stall warnings Message-ID: <20120904225153.GU2593@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120830185607.GA32148@linux.vnet.ibm.com> <1346352988-32444-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346352988-32444-10-git-send-email-paulmck@linux.vnet.ibm.com> <20120831182302.GH4259@jtriplet-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120831182302.GH4259@jtriplet-mobl1> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12090422-6148-0000-0000-0000094621EE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 31, 2012 at 11:23:02AM -0700, Josh Triplett wrote: > On Thu, Aug 30, 2012 at 11:56:23AM -0700, Paul E. McKenney wrote: > > From: "Paul E. McKenney" > > > > The print_other_cpu_stall() function accesses a number of rcu_node > > fields without protection from the ->lock. In theory, this is not > > a problem because the fields accessed are all integers, but in > > practice the compiler can get nasty. Therefore, the commit extends > > the existing critical section to cover the entire loop body. > > > > Signed-off-by: Paul E. McKenney > > --- > > kernel/rcutree.c | 6 ++++-- > > 1 files changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index 9f44749..fbe43b0 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -746,14 +746,16 @@ static void print_other_cpu_stall(struct rcu_state *rsp) > > rcu_for_each_leaf_node(rsp, rnp) { > > raw_spin_lock_irqsave(&rnp->lock, flags); > > ndetected += rcu_print_task_stall(rnp); > > - raw_spin_unlock_irqrestore(&rnp->lock, flags); > > - if (rnp->qsmask == 0) > > + if (rnp->qsmask == 0) { > > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > > continue; > > + } > > for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) > > if (rnp->qsmask & (1UL << cpu)) { > > print_cpu_stall_info(rsp, rnp->grplo + cpu); > > ndetected++; > > } > > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > > } > > Now that you've extended the lock over the rest of the loop body, I > think this would look much clearer if written without the continue and > duplicate lock release: > > ... > if (rnp->qsmask != 0) > for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) > .... > raw_spin_unlock_irqrestore(&rnp->lock, flags); > } And my Hollerith experience strikes again! ;-) Though this one seems more worthwhile, so I am making the change, conflicts permitting. Thanx, Paul