From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755606AbaKERlu (ORCPT ); Wed, 5 Nov 2014 12:41:50 -0500 Received: from e35.co.us.ibm.com ([32.97.110.153]:35391 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755269AbaKERln (ORCPT ); Wed, 5 Nov 2014 12:41:43 -0500 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: 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, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 02/10] rcu: Protect rcu_boost() lockless accesses with ACCESS_ONCE() Date: Wed, 5 Nov 2014 09:41:26 -0800 Message-Id: <1415209294-2534-2-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1415209294-2534-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20141105174109.GA1306@linux.vnet.ibm.com> <1415209294-2534-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14110517-0013-0000-0000-00000608C43E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. */ raw_spin_lock_irqsave(&rnp->lock, flags); -- 1.8.1.5