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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 D503FC2D0A3 for ; Mon, 9 Nov 2020 16:20:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7DAD82074F for ; Mon, 9 Nov 2020 16:20:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604938808; bh=oqLUZkDJovPnphDNZNNfXtQR+B26RG6pDlvnApy5MHQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=pSdCBZtIKaaMS2rNP5z2RIRalA32Z5rikpMjmg2vCV9IzRzy3MhHmm7Xy+Tl6T6m6 ZeAsZfINEHDhRX/K5bY1Nelv+xIlP6jqDjukMQHvyiz9h596+XefgYs1y9NdVjUqwl s/oBMvhjf9QL2mz6f/BjjHm7yv2oduxt04+3hM6s= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727774AbgKIQUH (ORCPT ); Mon, 9 Nov 2020 11:20:07 -0500 Received: from mail.kernel.org ([198.145.29.99]:48520 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726410AbgKIQUH (ORCPT ); Mon, 9 Nov 2020 11:20:07 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (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 A53B1206CB; Mon, 9 Nov 2020 16:20:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604938806; bh=oqLUZkDJovPnphDNZNNfXtQR+B26RG6pDlvnApy5MHQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=l3IWgbhDy1rVVerCwZSglLg4bgbYQHx6Y+06kRROZy1RDdKRBJBc6kV7DGkEMogP9 Vc+YcT+TMAoNbHcpjY6+Cw56kQ2Wdxy9dvnBVBQZoxirIIcgntok2+dpUmNhpmbLux VLwYF784LhGFQoHxGF5twyWQ0kUZpwnzyl+DadoE= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 5012F352264D; Mon, 9 Nov 2020 08:20:06 -0800 (PST) Date: Mon, 9 Nov 2020 08:20:06 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: rcu@vger.kernel.org, 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, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org Subject: Re: [PATCH tip/core/rcu 1/4] doc: Present the role of READ_ONCE() Message-ID: <20201109162006.GJ3249@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201105230444.GA18574@paulmck-ThinkPad-P72> <20201105230510.18660-1-paulmck@kernel.org> <20201109122133.GL2594@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201109122133.GL2594@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Mon, Nov 09, 2020 at 01:21:33PM +0100, Peter Zijlstra wrote: > On Thu, Nov 05, 2020 at 03:05:07PM -0800, paulmck@kernel.org wrote: > > From: "Paul E. McKenney" > > > > This commit adds an explanation of the special cases where READ_ONCE() > > may be used in place of a member of the rcu_dereference() family. > > I am confused, there is no actual difference between rcu_dereference() > and READ_ONCE() today. So we _may_ use READ_ONCE() at all times. > > Now granted, we probably don't want that, but that does leave me > somewhat confused vs the wording here. There is a difference from the viewpoint of both lockdep and sparse. Or am I missing your point? Thanx, Paul