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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 01E31C282DD for ; Fri, 10 Jan 2020 19:24:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D712B20848 for ; Fri, 10 Jan 2020 19:24:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728412AbgAJTYU (ORCPT ); Fri, 10 Jan 2020 14:24:20 -0500 Received: from mout.kundenserver.de ([217.72.192.73]:35603 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728106AbgAJTYT (ORCPT ); Fri, 10 Jan 2020 14:24:19 -0500 Received: from mail-qv1-f41.google.com ([209.85.219.41]) by mrelayeu.kundenserver.de (mreue108 [212.227.15.145]) with ESMTPSA (Nemesis) id 1Ml6du-1jWmM93TQ4-00lUgy; Fri, 10 Jan 2020 20:24:18 +0100 Received: by mail-qv1-f41.google.com with SMTP id o18so1273662qvf.1; Fri, 10 Jan 2020 11:24:17 -0800 (PST) X-Gm-Message-State: APjAAAXfCtqtVZa3zweztH807mcxq5nVQsUoitn16oXtfVsKebOMzTrf szWHIc2WM5zytaE3TI9HaOfEazifq1jEusyoX7w= X-Google-Smtp-Source: APXvYqzd2hmstZ9l10zTYEs+f7uDdN5MQZM9KWvb/cNLE8AYGII20Ive9ghFbtq0MLUH74D2qPmefmOPczx/DA0uGUI= X-Received: by 2002:a0c:d788:: with SMTP id z8mr152872qvi.211.1578684256605; Fri, 10 Jan 2020 11:24:16 -0800 (PST) MIME-Version: 1.0 References: <20200110165636.28035-1-will@kernel.org> <20200110165636.28035-6-will@kernel.org> In-Reply-To: <20200110165636.28035-6-will@kernel.org> From: Arnd Bergmann Date: Fri, 10 Jan 2020 20:24:00 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH 5/8] READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses To: Will Deacon Cc: "linux-kernel@vger.kernel.org" , linux-arch , Android Kernel Team , Michael Ellerman , Peter Zijlstra , Linus Torvalds , Segher Boessenkool , Christian Borntraeger , Luc Van Oostenryck Content-Type: text/plain; charset="UTF-8" X-Provags-ID: V03:K1:ev8K4YMvcdYPml3GY3aO/4/vuWKU7cZbfJmipe8dfz3JyngSvju Wv4NNUmZTSTTyU0E16+aJt3syYAiNy3NWp4ERPkdTDo0mcHbhhZZv7mzbn+HbP40vcFYe1Y KyQDlk1l2GqNLVtLXUi6HllsgidHr0AqBMLVu3JZuM6p9cQHJ/ZWPq0VndUsN5NcUld4iox S0AHYQQR99ROxBuMmdKMA== X-UI-Out-Filterresults: notjunk:1;V03:K0:wpkyqc6zofw=:ToNUCGqkTCirKuUdME33UK IhZ/Fkyf/Ux8dK5ivs4y0WMR76cYYUvMGSzo0GAV8rLea90c05nx/SWquKF3LtZ2glH2xfhLI kAPTK7CR1X6RoQQMU59O45BGJwyFnTR/BKF5sKjfoopx/hnTLeQYQGRvn13Wza3ikm0vtxHKJ fps6FiEoW45Vf3LGu5B00LiwN/k2pzFCMY0O5X++CXTaVA5lrCEtyzvM0m/7YgaszGwvtJphO jrlGo2YNinYzumLXEYjAHxavFHLZoSp/1/X++lEcGUsJqOpbPbEvkBMjo9gcnVzhePTv3NqBF uV3l/C6odOTgdyWJ8ThVJLd02EVEWLCNTV2TpFzZnEE77yCxjlO9UoQ0GBII1zLtKa3Ah2zlm 9XdyEJ5x2C1vz07TsIdTBC05j8kgm4plJsw4Q1bgVNh0UuiI+Tdhxtxyg9jhc9CZprmgdBzKM zy+EzZaoEV9U7aSkRQXr+tepXgNU7ZaMIDz+X6dpTrPVT8Tl44q7meUf+Flv1BMSjzoi4gTGd jlc6G/RJB+CDa1XNux+SN1VTYnB+vqNMFfnb5xGkFNLIiS1YvzTroupdI7AaBHz/PlOsbC8Ss VrBwj1Y+rV5ra7k0cYfT/0Y2cCZiJ4xlXi17jk0CA4ooH8YRCagawtftvS5jFoKeI/iwbd/Yr hX07tjd+pRUtWpNF/OJM/7taBcDcvdwjKE+ruyQvdbctR1F2oH51k4U6zLSx/yqWEAkJiB3Zd VZDHwBswTCCzW+D/PTdQcsPUP/1wbXi0h1Xn4dU4x5GjnqKW3dl7iTpZi6fRiD/02LosMgiev ZdqNQV4UlnOUA31tU/tGLzXuuHGlIyRA0D3Q6KN+1K8MT+sGke4itjh/JndDYKlHhb5BjnZpb MYZvSJlBKUu2g6XzrbCg== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 10, 2020 at 5:56 PM Will Deacon wrote: > +/* > + * Use __READ_ONCE() instead of READ_ONCE() if you do not require any > + * atomicity or dependency ordering guarantees. Note that this may result > + * in tears! > + */ > +#define __READ_ONCE(x) (*(volatile typeof(x) *)&(x)) > + This probably allows writing extern int i; __READ_ONCE(i) = 1; and not get a warning for it. How about also casting to 'const'? Arnd