From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932299AbbCCREL (ORCPT ); Tue, 3 Mar 2015 12:04:11 -0500 Received: from e39.co.us.ibm.com ([32.97.110.160]:41763 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932200AbbCCREG (ORCPT ); Tue, 3 Mar 2015 12:04:06 -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 02/12] rcu_tree: Avoid touching rnp->completed when a new GP is started Date: Tue, 3 Mar 2015 09:03:45 -0800 Message-Id: <1425402235-11061-2-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1425402235-11061-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20150303170329.GA8456@linux.vnet.ibm.com> <1425402235-11061-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15030317-0033-0000-0000-000003D97A6F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Lai Jiangshan In rcu_gp_init(), rnp->completed equals to rsp->completed in THEORY, we don't need to touch it normally. If something goes wrong, it will complain and fixup rnp->completed and avoid oops. This commit thus avoids the normal needless store to rnp->completed. Signed-off-by: Lai Jiangshan Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 48d640ca1a05..077d0b700f74 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1757,8 +1757,8 @@ static int rcu_gp_init(struct rcu_state *rsp) rcu_preempt_check_blocked_tasks(rnp); rnp->qsmask = rnp->qsmaskinit; ACCESS_ONCE(rnp->gpnum) = rsp->gpnum; - WARN_ON_ONCE(rnp->completed != rsp->completed); - ACCESS_ONCE(rnp->completed) = rsp->completed; + if (WARN_ON_ONCE(rnp->completed != rsp->completed)) + ACCESS_ONCE(rnp->completed) = rsp->completed; if (rnp == rdp->mynode) (void)__note_gp_changes(rsp, rnp, rdp); rcu_preempt_boost_start_gp(rnp); -- 1.8.1.5