From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 54BE0C433E6 for ; Wed, 6 Jan 2021 01:27:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1422022CB9 for ; Wed, 6 Jan 2021 01:27:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726273AbhAFB1S (ORCPT ); Tue, 5 Jan 2021 20:27:18 -0500 Received: from mail.kernel.org ([198.145.29.99]:33674 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725919AbhAFB1A (ORCPT ); Tue, 5 Jan 2021 20:27:00 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 4E0E2230FB; Wed, 6 Jan 2021 01:26:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1609896379; bh=BZakVGmmFZs3Nsx5FTiFBS7dxQEqfjcF87UEFxArC8w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JPEnMbj1Cw31ti0w9ebdZpiQlulG+5FhUVoDYqmXx0qsEusw8LyIQtgspSJjR1yS4 8fjqRJoBVIG5gMvOeWECR+v+r44KvScvFqu8VKJ+5ZZQ1kKcen/INmVbVPHenWStY0 N9fyLOsHxh1CAX1x3X16mXmwJH9+yDV3L9pbcMpbq+5t28GM9qKQXeGN/7n7s1ju9p 46hTIiJZChb83kP+lZnzEv8ohDSh6L2ouWxchU1dD/JG4qSGdkutEksOZxrpwWalpZ rh7FBJBVK2BDnkXFVwFBcdS59Fz0OdV8kQ86s64I+gXbuiVeq/pRfbRvh/MjUvDX4o QK5mGIFt6gI1A== From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.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, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E . McKenney" Subject: [PATCH tip/core/rcu 4/6] rcu/tree: segcblist: Remove redundant smp_mb()s Date: Tue, 5 Jan 2021 17:26:15 -0800 Message-Id: <20210106012617.14122-4-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20210106012541.GA13972@paulmck-ThinkPad-P72> References: <20210106012541.GA13972@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Joel Fernandes (Google)" The full memory barriers in rcu_segcblist_enqueue() and in rcu_do_batch() are not needed because rcu_segcblist_add_len(), and thus also rcu_segcblist_inc_len(), already includes a memory barrier *before* and *after* the length of the list is updated. This commit therefore removes these redundant smp_mb() invocations. Reviewed-by: Frederic Weisbecker Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- kernel/rcu/rcu_segcblist.c | 1 - kernel/rcu/tree.c | 1 - 2 files changed, 2 deletions(-) diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c index 0504fc83..5059b61 100644 --- a/kernel/rcu/rcu_segcblist.c +++ b/kernel/rcu/rcu_segcblist.c @@ -327,7 +327,6 @@ void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp, struct rcu_head *rhp) { rcu_segcblist_inc_len(rsclp); - smp_mb(); /* Ensure counts are updated before callback is enqueued. */ rcu_segcblist_inc_seglen(rsclp, RCU_NEXT_TAIL); rhp->next = NULL; WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rhp); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index cc6f379..b0fb654 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2523,7 +2523,6 @@ static void rcu_do_batch(struct rcu_data *rdp) /* Update counts and requeue any remaining callbacks. */ rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl); - smp_mb(); /* List handling before counting for rcu_barrier(). */ rcu_segcblist_add_len(&rdp->cblist, -count); /* Reinstate batch limit if we have worked down the excess. */ -- 2.9.5