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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 89D6EC55178 for ; Mon, 26 Oct 2020 12:01:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3C54122265 for ; Mon, 26 Oct 2020 12:01:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603713675; bh=qdf3h/zutIWsyOkbj2VUmEclleb3GPZkmclXVLokVKY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=OqqRk+dp1YOynKQy+Ex6bTVXVLpttepWeKo0jwLFn+YomJpSYVTn2YfThXqnNBFcp OICfGrQvXJOQJAI8KjC1xaxkT75D/D75X0ggJnAOc+rkg/QvW7eQr16VBeYQbHsbpn /nJGHJ4lQrT864UCm7C0pBN1tKTMupVbNe99RJY0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1774636AbgJZMBO (ORCPT ); Mon, 26 Oct 2020 08:01:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:46542 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1774626AbgJZMBJ (ORCPT ); Mon, 26 Oct 2020 08:01:09 -0400 Received: from localhost (unknown [176.177.109.29]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 42D5B22281; Mon, 26 Oct 2020 12:01:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603713668; bh=qdf3h/zutIWsyOkbj2VUmEclleb3GPZkmclXVLokVKY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rbJZNQYTer006cByNMjTPUHvd3UNK0MlXIC2nTyROKg4alhernbaDnHKL74hstsjT Dn7yIiWD90IZv5iYoHOtjzDB/m7dLXQtXprxPZN2Vzcv/OiW16YxIPcTfh+nfBHUI5 GAS3RubBikxT4OPWhVzsI6KHZM1elJyIOtwK7/ro= Date: Mon, 26 Oct 2020 13:01:06 +0100 From: Frederic Weisbecker To: "Joel Fernandes (Google)" Cc: linux-kernel@vger.kernel.org, Josh Triplett , Lai Jiangshan , Marco Elver , Mathieu Desnoyers , "Paul E. McKenney" , rcu@vger.kernel.org, Steven Rostedt , "Uladzislau Rezki (Sony)" , fweisbec@gmail.com, neeraj.iitr10@gmail.com Subject: Re: [PATCH v8 5/6] rcu/tree: segcblist: Remove redundant smp_mb()s Message-ID: <20201026120106.GF104441@lothringen> References: <20201021190813.3005054-1-joel@joelfernandes.org> <20201021190813.3005054-6-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201021190813.3005054-6-joel@joelfernandes.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 65;6003;1cOn Wed, Oct 21, 2020 at 03:08:12PM -0400, Joel Fernandes (Google) wrote: > This memory barrier is not needed as rcu_segcblist_add_len() already > includes a memory barrier *before* the length of the list is updated. *before* and *after*. As you have both cases below. Thanks > > Same reasoning for rcu_segcblist_enqueue(). > > Signed-off-by: Joel Fernandes (Google) > --- > 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 19ff82b805fb..f0fcdf9d0f7f 100644 > --- a/kernel/rcu/rcu_segcblist.c > +++ b/kernel/rcu/rcu_segcblist.c > @@ -268,7 +268,6 @@ 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 346a05506935..6c6d3c7036e6 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2525,7 +2525,6 @@ 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. */ > -- > 2.29.0.rc1.297.gfa9743e501-goog >