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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 9F9D7C433E0 for ; Sun, 27 Dec 2020 23:41:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 46A83224F9 for ; Sun, 27 Dec 2020 23:41:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726340AbgL0Xlh (ORCPT ); Sun, 27 Dec 2020 18:41:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38374 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726289AbgL0Xlg (ORCPT ); Sun, 27 Dec 2020 18:41:36 -0500 Received: from mail-lf1-x132.google.com (mail-lf1-x132.google.com [IPv6:2a00:1450:4864:20::132]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B3B8C061794 for ; Sun, 27 Dec 2020 15:40:56 -0800 (PST) Received: by mail-lf1-x132.google.com with SMTP id o19so20524932lfo.1 for ; Sun, 27 Dec 2020 15:40:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=2g/tw1CfRfSS28JS/E5UEQtXF4RogkgHtVGCAK+cqLg=; b=hmk+nXUKCLprIED87lepHbqNo9/5jDD/zPgpKqfdGUAfyt5eQN8IPSx+3kRgMMUEUo WENraXsqaYlObe0ODWSqZ3r0hKg3rOLnExPsZHKeesNCNNc0ihW35MuIOnqY4fkAS3BZ dhMQhiHVyIoLXszKYVzPhcMPZpMIyqz7BTmxg= 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=2g/tw1CfRfSS28JS/E5UEQtXF4RogkgHtVGCAK+cqLg=; b=E3JfffUfv9CMn6lS5WFUEzasa/uaWFCQzZoalZyQZnZutRtzFS8MHZK8s35Rdp6tjc dUxVqniO74pC47ONP1hMRnlI94qalzoeUf1Jnl5xJqHX9qmtBwBYLICxq0PItAjc8MAF vd+a/OXeYhnvm607iaHgbiUBwqZnTHWxnf16lMQaI5Oe7MyyEWVtnZujcN6dpw34YzyC XOgS6LKpeGEpD2wgLPp+h+oD1+dou5CtdDmcW1kxbn17E1MU5B1UXthS07KEmXGxLnOz cgZRf1qY9NyHX8EBT/tKuTQw0ejbONDfNh8HUp83dfEpx7otj1zwzGO+M+DZe9YGDQef faYw== X-Gm-Message-State: AOAM533NR45whXk65F7Q2kdZGj3t1eQoCEYkm620ZfjFE8yqpnPRJQNO 09/mOntHr0MSKzNT7vDBj0zWja0ikDeTKA== X-Google-Smtp-Source: ABdhPJw5xn0+MKwDqAUrME+yR0dHR0L+PtJbFosr8HJHXTKHpahDCPGSu4wlAcVhhggU8bNeJYpWmQ== X-Received: by 2002:a05:6512:3e6:: with SMTP id n6mr17346428lfq.262.1609112454075; Sun, 27 Dec 2020 15:40:54 -0800 (PST) Received: from mail-lf1-f42.google.com (mail-lf1-f42.google.com. [209.85.167.42]) by smtp.gmail.com with ESMTPSA id y13sm5161653lfg.189.2020.12.27.15.40.52 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 27 Dec 2020 15:40:52 -0800 (PST) Received: by mail-lf1-f42.google.com with SMTP id o17so20476312lfg.4 for ; Sun, 27 Dec 2020 15:40:52 -0800 (PST) X-Received: by 2002:a2e:9ad7:: with SMTP id p23mr19677994ljj.465.1609112452213; Sun, 27 Dec 2020 15:40:52 -0800 (PST) MIME-Version: 1.0 References: <20201225113157.e7hmluffh56fszfc@box> <20201226204335.dikqkrkezqet6oqf@box> <20201226224016.dxjmordcfj75xgte@box> In-Reply-To: From: Linus Torvalds Date: Sun, 27 Dec 2020 15:40:36 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting To: Hugh Dickins , Andrew Morton Cc: Damian Tometzki , "Kirill A. Shutemov" , Matthew Wilcox , "Kirill A. Shutemov" , Will Deacon , Linux Kernel Mailing List , Linux-MM , Linux ARM , Catalin Marinas , Jan Kara , Minchan Kim , Vinayak Menon , Android Kernel Team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Dec 27, 2020 at 3:12 PM Linus Torvalds wrote: > > Ok, your fix for that folded in, and here's yet another version. Still not good. I don't know what happened, but the change of - vm_fault_t ret = 0; + vm_fault_t ret; is very very wrong. The next user is + if (!(vma->vm_flags & VM_SHARED)) + ret = check_stable_address_space(vma->vm_mm); + if (ret) + return ret; so now 'ret' will potentially be used uninitialized (although this is the kind of thing that a compiler might almost accidentally end up fixing - with a single dominating assignment, I could imagine the compiler moving the test to that assignment and thus "fixing" the code without really even meaning to). I think Kirill was intending to move the "if (ret)" up into the path that sets it, IOW something like + if (!(vma->vm_flags & VM_SHARED)) { + ret = check_stable_address_space(vma->vm_mm); + if (ret) + return ret; + } instead. But that patch as-is is broken. Kirill? Linus