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=-13.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 DA8D3C433EF for ; Mon, 13 Sep 2021 20:52:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BFBCC6108B for ; Mon, 13 Sep 2021 20:52:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347873AbhIMUxh (ORCPT ); Mon, 13 Sep 2021 16:53:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50098 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243622AbhIMUxN (ORCPT ); Mon, 13 Sep 2021 16:53:13 -0400 Received: from mail-lj1-x22d.google.com (mail-lj1-x22d.google.com [IPv6:2a00:1450:4864:20::22d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 126CEC0613BB for ; Mon, 13 Sep 2021 13:50:30 -0700 (PDT) Received: by mail-lj1-x22d.google.com with SMTP id s3so19585780ljp.11 for ; Mon, 13 Sep 2021 13:50:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=8TVqbn8thZCqMP/VrYd9m008Vn/d1QsljDuZZA3Cj3U=; b=Kx+QXs7/Gqu+0fT01IBf7AvtFuuKzukMCBr8Uj8Tlirfgy3sBlDb/0dgxW8i2fm4ki Cr2wjOBudyMAbTz6hMk9v40PhWKj9nMcIvmb30kyKFZB5RsdvaSnLonYQoWCJky9Fn/q rvmHHz1xfT6sAANA+Cql145bvCNIa1CwpBa7ThFjKt5zw9vKElWhqhFhEUwiaxOgfZ8Z mc6ZDYEM+0S6oMqPrZMSE/Xi4nZl2oaQoisz2wKEDinJKmadJxfu8MSthUEwUNPCWeqH fluefePE4KH12STgQsgozYhaHaImiPkP9T36zeeUIgpXLdwXCdryY+34zNJ9CWrttP02 lFrQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=8TVqbn8thZCqMP/VrYd9m008Vn/d1QsljDuZZA3Cj3U=; b=pe+MOCvKICChjuR7T5rR94GDOIRoeGF5nwNxBtQX4AZtwIMccobywOVnRkvj9uLAwb /Asw2ukvN9ADsEJgz2/ChOKWowSxqkXS5Qm9skFewyMVBUn7DZM0vV+3OjO5J7B8MQca M6dohd7+gkLAeyuDudbtH+zgE0BN5wsT0i+PIbv7wu9s7Wk24cYl7R9Xd/eM5Y7xLN/g JQGKo+OXOPx/WCy9r+PtJBFJBiaiCVA74GLN6grzxAT68Ft5C7LKEj4kL5nK+WEA/QLn YYArw81hagWtfsLH63B4ab5GPFhhXKulZ/Rqmh4r4HIyDvmCcxsCWEYL8DJO0JuYZ7ZQ UxBA== X-Gm-Message-State: AOAM530P9ybqvsGSDsa94bkR5FN8gYrxh0qhoSkbdHEIrN3TkAo6qVhj 2vMZqHxzdhpJX8VCt+ngLP0ODj2cT6igwpwYmKViGw== X-Google-Smtp-Source: ABdhPJy0QpA58fznBHhrAEHivK9kgUxh+cUT8ejPHdCeOcbTpFXS2375qe5rVNCNeV1nKlpokjSe4FcWCpoMJsDrm+0= X-Received: by 2002:a05:651c:54d:: with SMTP id q13mr12530242ljp.526.1631566228215; Mon, 13 Sep 2021 13:50:28 -0700 (PDT) MIME-Version: 1.0 References: <20210913131113.390368911@linuxfoundation.org> <20210913131114.028340332@linuxfoundation.org> In-Reply-To: From: Nick Desaulniers Date: Mon, 13 Sep 2021 13:50:17 -0700 Message-ID: Subject: Re: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in __nbd_ioctl() To: Linus Torvalds Cc: Arnd Bergmann , Sedat Dilek , Greg Kroah-Hartman , Naresh Kamboju , Nathan Chancellor , Baokun Li , open list , linux-stable , Hulk Robot , Josef Bacik , Jens Axboe , Sasha Levin , clang-built-linux , lkft-triage@lists.linaro.org, llvm@lists.linux.dev, Kees Cook Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 13, 2021 at 1:42 PM Linus Torvalds wrote: > > On Mon, Sep 13, 2021 at 1:16 PM Nick Desaulniers > wrote: > > > > Do we have access to _Generic in GCC 4.9? > > We've ended up using it unconditionally since last year, so yes. Sorry, grepping would have taken < 1s. I'm very lazy. http://threevirtues.com/ > > In fact, the compiler version tests got removed when we raised the gcc > version requirement to 4.9 in commit 6ec4476ac825 ("Raise gcc version > requirement to 4.9"): > > "In particular, raising the minimum to 4.9 means that we can now just > assume _Generic() exists, which is likely the much better replacement > for a lot of very convoluted built-time magic with conditionals on > sizeof and/or __builtin_choose_expr() with same_type() etc" > > but we haven't used it much since. > > The "seqprop" code for picking the right lock for seqlock is perhaps > the main example, and staring at that code will make you go blind, so > look away. Looking at my patch: https://lore.kernel.org/stable/20210913203201.1844253-1-ndesaulniers@google.com/ I don't think _Generic helps us in the case of dispatching based on the result of is_signed_type() (the operands could undergo type promotion, so we'd need lots of cases that are more concisely covered by is_signed_type()). It could replace the nested checks in div_64 with nested _Generics, I think. Not sure it's a huge win for readability. Maybe cut the number of expansions of the parameters in half though. Let me give it a try just to see what it looks like. -- Thanks, ~Nick Desaulniers