From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757186Ab2IFO4w (ORCPT ); Thu, 6 Sep 2012 10:56:52 -0400 Received: from casper.infradead.org ([85.118.1.10]:46028 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757107Ab2IFO4r convert rfc822-to-8bit (ORCPT ); Thu, 6 Sep 2012 10:56:47 -0400 Message-ID: <1346943078.18408.29.camel@twins> Subject: Re: [PATCH tip/core/rcu 10/15] rcu: Protect rcu_node accesses during CPU stall warnings From: Peter Zijlstra To: "Paul E. McKenney" 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, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org Date: Thu, 06 Sep 2012 16:51:18 +0200 In-Reply-To: <1346352988-32444-10-git-send-email-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> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2012-08-30 at 11:56 -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); > } You now cover printk() and all that that can call with a RCU lock.. is this a good thing?