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=-8.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 27ECEC33CB1 for ; Fri, 17 Jan 2020 13:15:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EEB4B20728 for ; Fri, 17 Jan 2020 13:15:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="phe1Ud2o" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726954AbgAQNPB (ORCPT ); Fri, 17 Jan 2020 08:15:01 -0500 Received: from mail-ot1-f42.google.com ([209.85.210.42]:39839 "EHLO mail-ot1-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726574AbgAQNPA (ORCPT ); Fri, 17 Jan 2020 08:15:00 -0500 Received: by mail-ot1-f42.google.com with SMTP id 77so22480420oty.6 for ; Fri, 17 Jan 2020 05:15:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=B8YqwuFYQqcgYYrogodMJhZN7j+MHKf9rIlBL0O/Le8=; b=phe1Ud2oxwDPz6N0qGWXhYFzGha1cekzFvcn3g626qlUYghuyTbxgeFkLbD/M/5L2u FDYTHp9qH37eL4oqnFRBAXta5mf/ffxwB4CRYjCptTn0qENxhEnuJ6sd/k/c5WjQtL3l CZK7j9ZJcq40q1mQa/jNGhIl8VicJfvINi+VTqNF9qMX85UYRNemMrGHv6Y80fNbk6dg S9PPuTsUhR6lSiS6eVa+Gbu3kWZBLzmYXabHgR1/Uj8EbZ/xevu89+zvdF3lhTPSyKkD PaFZsgRegpuHk3NdVQ+8Daz+cDXqVbLvfaHQH+1GTrWlCrdFvn5XQvguxBKRfdkeZq/s GNkQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=B8YqwuFYQqcgYYrogodMJhZN7j+MHKf9rIlBL0O/Le8=; b=Vc5ylP6Kf7+IzSJvIY8bNi8ALiOTgYZDlYSQkrENXjEknjMCqaU3g9kcmHiLkeynTG 5ct/K2IOI2d8J86njod5Sw2WNOiRwbya3dHB9jXOHjx1Fd1l4cetadAHEVsufDoCxms+ PP/cpvQlYacsdAmDOtyR2q6UyoFn5W2ghT4Xv4fDPrnEe7iYHKzhMXRxdwdjjq25b/Xk LJOKt51hmLHpp5/WKOldttO/zWYjccJVDzIFVnwOvg5SVwRcPkV7zzhLVTY5Hjcw+7VX qL79hKhACUmN5oKd7/Su5RQzIrk3bPNTWok2ISa2B3dp33O0LnYi8qQE/Z2IhtBZRkG1 2NPQ== X-Gm-Message-State: APjAAAXZDcQKm3n0BB3/L3ayrTfHKMitq5kLQLbn5HIoOl0FzjIPF17n KlAXcVVSQY1fz92uoIMNPgHg2nP+LRY8iCijsqppxA== X-Google-Smtp-Source: APXvYqynE9NXU66Nq3blnE6X5VRCzGBBlylly2otE6jy/NdZxB8n4qYZlqLeRV0gBLCzSb/O+tcyFH8cZEHX5B05W4k= X-Received: by 2002:a9d:588c:: with SMTP id x12mr5863094otg.2.1579266899985; Fri, 17 Jan 2020 05:14:59 -0800 (PST) MIME-Version: 1.0 References: <20200115165749.145649-1-elver@google.com> In-Reply-To: From: Marco Elver Date: Fri, 17 Jan 2020 14:14:48 +0100 Message-ID: Subject: Re: [PATCH -rcu] asm-generic, kcsan: Add KCSAN instrumentation for bitops To: Arnd Bergmann Cc: "Paul E. McKenney" , Andrey Konovalov , Alexander Potapenko , Dmitry Vyukov , kasan-dev , "linux-kernel@vger.kernel.org" , Michael Ellerman , christophe leroy , Daniel Axtens , linux-arch Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 17 Jan 2020 at 13:25, Arnd Bergmann wrote: > > On Wed, Jan 15, 2020 at 9:50 PM Marco Elver wrote: > > On Wed, 15 Jan 2020 at 20:55, Arnd Bergmann wrote: > > > On Wed, Jan 15, 2020 at 8:51 PM Marco Elver wrote: > > > > On Wed, 15 Jan 2020 at 20:27, Arnd Bergmann wrote: > > > Are there any that really just want kasan_check_write() but not one > > > of the kcsan checks? > > > > If I understood correctly, this suggestion would amount to introducing > > a new header, e.g. 'ksan-checks.h', that provides unified generic > > checks. For completeness, we will also need to consider reads. Since > > KCSAN provides 4 check variants ({read,write} x {plain,atomic}), we > > will need 4 generic check variants. > > Yes, that was the idea. > > > I certainly do not feel comfortable blindly introducing kcsan_checks > > in all places where we have kasan_checks, but it may be worthwhile > > adding this infrastructure and starting with atomic-instrumented and > > bitops-instrumented wrappers. The other locations you list above would > > need to be evaluated on a case-by-case basis to check if we want to > > report data races for those accesses. > > I think the main question to answer is whether it is more likely to go > wrong because we are missing checks when one caller accidentally > only has one but not the other, or whether they go wrong because > we accidentally check both when we should only be checking one. > > My guess would be that the first one is more likely to happen, but > the second one is more likely to cause problems when it happens. Right, I guess both have trade-offs. > > As a minor data point, {READ,WRITE}_ONCE in compiler.h currently only > > has kcsan_checks and not kasan_checks. > > Right. This is because we want an explicit "atomic" check for kcsan > but we want to have the function inlined for kasan, right? Yes, correct. > > My personal preference would be to keep the various checks explicit, > > clearly opting into either KCSAN and/or KASAN. Since I do not think > > it's obvious if we want both for the existing and potentially new > > locations (in future), the potential for error by blindly using a > > generic 'ksan_check' appears worse than potentially adding a dozen > > lines or so. > > > > Let me know if you'd like to proceed with 'ksan-checks.h'. > > Could you have a look at the files I listed and see if there are any > other examples that probably a different set of checks between the > two, besides the READ_ONCE() example? All the user-copy related code should probably have kcsan_checks as well. > If you can't find any, I would prefer having the simpler interface > with just one set of annotations. That's fair enough. I'll prepare a v2 series that first introduces the new header, and then applies it to the locations that seem obvious candidates for having both checks. Thanks, -- Marco