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=-13.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 BC48CCA9EBB for ; Thu, 24 Oct 2019 13:58:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F6472166E for ; Thu, 24 Oct 2019 13:58:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ojoJPg1v" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393870AbfJXN6y (ORCPT ); Thu, 24 Oct 2019 09:58:54 -0400 Received: from mail-qk1-f196.google.com ([209.85.222.196]:42354 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727811AbfJXN6y (ORCPT ); Thu, 24 Oct 2019 09:58:54 -0400 Received: by mail-qk1-f196.google.com with SMTP id m4so6541597qke.9 for ; Thu, 24 Oct 2019 06:58:53 -0700 (PDT) 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=UOruI0JrGFz7xrLotlBY15Zel47+fi3BtuX0TPe8v+s=; b=ojoJPg1vybYzGTONg5L7cUYX3/GVoymSo7uGRPUG8kfU1ldQOrWGDfUvzrRLML+CTR UQL7SYjkigtIrTndCk+J0sqzk13K/85JxFkzAbqUaCFWWDZI4YYySteGjhZMidl2qheO aZxZgnpPgNsSK15IiJgvGT5BdDnuUmbFM1hjK4ivbLNK6cThuC4D8v+qljKLKDcGN3/P TrIaok3VoSEirnQkvCNRUntWEgh1Q49kKUWXK0nmXE6yxBqs+k62GJVES6/h/H3bF44w DrykRV0/8HC4e6JMdM4e6DUtDUDxGsrOEfu5/vj1EUsnQnuoqikCl9AuRm+yaCsOmatn HEpQ== 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=UOruI0JrGFz7xrLotlBY15Zel47+fi3BtuX0TPe8v+s=; b=FFuj0fOYaYZEFRf/UCfvytGjVbsgyYrFVe4XGspAUTAGoqyRF9qrJMQbTeO5xoHtgE rzBG4HHNzHQojMFwjLyL9O4Wh9+584vkis1UokY93AJPYeTGJ2m8u2QhF3PYJe3aJdRO dTMT8FJYAvVPHQj6Zd2xPDykFfE9AHtJLmHnReykp3019G+BbEtg3zPoe8Dw+bdVoWBQ DO6Y8TVe6BsvA8prdp42D0MwBVOVcu5mYmbqJYsfSlr2F5KVRLJwMXQGEVJ3+X6noBjj Qub7refQ7dYUGoQ3dK0toLuRfv3w+1ri6R5/YRe+pgVJY1SdEyoLT4+WOfjrfmx1RXxt y5Ag== X-Gm-Message-State: APjAAAXDuhL2l+m/fvc3e/P8TpUH/OtU0f9JQ3C4/HejgtlNN5OTHSK1 mdk6w4EbBxD9LRcmt/VQsOC3zlm0taT4pIxQYHu2wA== X-Google-Smtp-Source: APXvYqyJH8mQi7kWDAjmkW7fqPexv//gkSatB3x6zm5BjqDBwjBozeI+h5HyB+gfDOt4dAGZI+IarZp2cnkR7axleZ8= X-Received: by 2002:a05:620a:2158:: with SMTP id m24mr14081580qkm.250.1571925532851; Thu, 24 Oct 2019 06:58:52 -0700 (PDT) MIME-Version: 1.0 References: <20191009114809.8643-1-christian.brauner@ubuntu.com> <20191021113327.22365-1-christian.brauner@ubuntu.com> <20191023121603.GA16344@andrea.guest.corp.microsoft.com> <20191024113155.GA7406@andrea.guest.corp.microsoft.com> <20191024130502.GA11335@andrea.guest.corp.microsoft.com> <20191024134319.GA12693@andrea.guest.corp.microsoft.com> In-Reply-To: <20191024134319.GA12693@andrea.guest.corp.microsoft.com> From: Dmitry Vyukov Date: Thu, 24 Oct 2019 15:58:40 +0200 Message-ID: Subject: Re: [PATCH v6] taskstats: fix data-race To: Andrea Parri Cc: Christian Brauner , Will Deacon , LKML , bsingharora@gmail.com, Marco Elver , stable , syzbot , syzkaller-bugs 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 Thu, Oct 24, 2019 at 3:43 PM Andrea Parri wrote: > > > But why? I think kernel contains lots of such cases and it seems to be > > officially documented by the LKMM: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/memory-model/Documentation/explanation.txt > > address dependencies and ppo > > Well, that same documentation also alerts about some of the pitfalls > developers can incur while relying on dependencies. I'm sure you're > more than aware of some of the debate surrounding these issues. I thought that LKMM is finally supposed to stop all these centi-threads around subtle details of ordering. And not we finally have it. And it says that using address-dependencies is legal. And you are one of the authors. And now you are arguing here that we better not use it :) Can we have some black/white yes/no for code correctness reflected in LKMM please :) If we are banning address dependencies, don't we need to fix all of rcu uses?