From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756148AbbAHJln (ORCPT ); Thu, 8 Jan 2015 04:41:43 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:53349 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752756AbbAHJlk (ORCPT ); Thu, 8 Jan 2015 04:41:40 -0500 Date: Thu, 8 Jan 2015 10:41:02 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: Re: [PATCH tip/core/rcu 01/14] rcu: Protect rcu_boost() lockless accesses with ACCESS_ONCE() Message-ID: <20150108094102.GD29390@twins.programming.kicks-ass.net> References: <20150107173215.GA897@linux.vnet.ibm.com> <1420651953-2651-1-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1420651953-2651-1-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 07, 2015 at 09:32:20AM -0800, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > This commit prevents random compiler optimizations by applying > ACCESS_ONCE() to lockless accesses. > > Signed-off-by: Paul E. McKenney > --- > kernel/rcu/tree_plugin.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index 3ec85cb5d544..d59913ef8360 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -1127,7 +1127,8 @@ static int rcu_boost(struct rcu_node *rnp) > struct task_struct *t; > struct list_head *tb; > > - if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) > + if (ACCESS_ONCE(rnp->exp_tasks) == NULL && > + ACCESS_ONCE(rnp->boost_tasks) == NULL) > return 0; /* Nothing left to boost. */ Didn't we just obsolete ACCESS_ONCE with that {READ,WRITE}_ONCE stuff?