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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 92270FA372A for ; Wed, 16 Oct 2019 15:32:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C67F218DE for ; Wed, 16 Oct 2019 15:32:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571239962; bh=RPHFakt8qph9Wb04jfbmvqI99+/VnGsa3iwgaOZOEsI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=AdmzT6KvXFkuHxUk7zhyA1ZbVSgMvcesXnzKABfOzqll733rAT6U7rDKId01EZv3A ifn9oG6EFXoylBup7LUkAeQ60lm06zIJYN7zNO4w/gjR5mkM89TCaEJ7k7HegnHNCL 4pmFfv2tUw39VWihSKmcv+lPo6V4YMhGRZF5crHg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404988AbfJPPci (ORCPT ); Wed, 16 Oct 2019 11:32:38 -0400 Received: from mail-qk1-f194.google.com ([209.85.222.194]:34008 "EHLO mail-qk1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726332AbfJPPci (ORCPT ); Wed, 16 Oct 2019 11:32:38 -0400 Received: by mail-qk1-f194.google.com with SMTP id q203so23161583qke.1; Wed, 16 Oct 2019 08:32:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=T9N8Qt/Q4T/fLDKFrE/yGjdsJz9c4IKV5iMQVuzGrps=; b=uR+B/8KpPRzIhOBAr5vomaF58ezGmJX/eSypGMHunaNAhefJay3pXHyQMlfeT33DY2 E7CYU5KMl9Bvj6oHq9PBQ/vQ4QhvoLaD8r9wy3Id7EKa6ZnUkh9C8r0M1g82ZyAAcRsA F8+Xxp3LqG/0rsTC+TCAaLPer+M4sVHPnYCFLSQ8AgEKp+5dkJ5KUf5oSjb4BDsB9VnN LTdQU3BkzHyE+SgCrKzT8ogPqp79w2Z45xmDJ2QbmKgqdd1vmbWHGQW5kdpch5QSKCt5 9LN25GRra8d834gUX5t4Z/INq89v6v7FkHZNuYvqadr1h9sT7s7zYSlvpz+zY8zONofD hXIg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=T9N8Qt/Q4T/fLDKFrE/yGjdsJz9c4IKV5iMQVuzGrps=; b=TahZLGn8FfS68bbu4SCx9zK+NuY4PXmWieaqMVzW8thWVJo9cAmB79UgEAlf50cM9+ A9orCeUJ669l72Pj0cT5sD1J+Jr3C5hzO1Qs8RjrZtO+/jVYHl9ioLwSqT8JZFRQaY2k pe8VRrKN3qJFnXfwsse3uo+9LPyg52GF7Dgensavu6mp+IMNxQYLfUfEYnKshBBhahZi d8F5luQLGc94pWdlBFVIer1vT4S0ozto4+bwXIZwqL8OdKXTcTzYwcRh6DdaSx4IRLfb ZM4xqIX5XQzUqEWWfzLOdiJTSujYm7NZxhELOcY+KHy87o0hRwkfjMobMHd6c+K+gPPn 0nzA== X-Gm-Message-State: APjAAAXg2NsYSXtnHBkticKPKQ+LKMyF+7FxlNxZ0TFD4RoY+8yC4Uia aLBrVmW5SzJU1tdDPcU4MX0= X-Google-Smtp-Source: APXvYqzyFvjB0Qdu/707bwgi1BqkvK7HYcGOwQw/+HX2xBFJ+Ju9kRmlElS1taWq5eKHN+mn/sFduw== X-Received: by 2002:a37:4151:: with SMTP id o78mr38324867qka.263.1571239956891; Wed, 16 Oct 2019 08:32:36 -0700 (PDT) Received: from localhost ([2620:10d:c091:500::1:2d57]) by smtp.gmail.com with ESMTPSA id o14sm16778400qtk.52.2019.10.16.08.32.35 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 16 Oct 2019 08:32:36 -0700 (PDT) Date: Wed, 16 Oct 2019 08:32:34 -0700 From: Tejun Heo To: Aleksa Sarai Cc: Li Zefan , Johannes Weiner , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] cgroup: pids: use {READ,WRITE}_ONCE for pids->limit operations Message-ID: <20191016153234.GO18794@devbig004.ftw2.facebook.com> References: <20191012010539.6131-1-cyphar@cyphar.com> <20191014154136.GF18794@devbig004.ftw2.facebook.com> <20191014155931.jl7idjebhqxb3ck3@yavin.dot.cyphar.com> <20191014163307.GG18794@devbig004.ftw2.facebook.com> <20191016083218.ttsaqnxpjh5i5bgv@yavin.dot.cyphar.com> <20191016142756.GN18794@devbig004.ftw2.facebook.com> <20191016152946.34j5x45ko5auhv3g@yavin.dot.cyphar.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191016152946.34j5x45ko5auhv3g@yavin.dot.cyphar.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org Hello, On Thu, Oct 17, 2019 at 02:29:46AM +1100, Aleksa Sarai wrote: > > Hah, where is it saying that? > > Isn't that what this says: > > > Therefore, if you find yourself only using the Non-RMW operations of > > atomic_t, you do not in fact need atomic_t at all and are doing it > > wrong. > > Doesn't using just atomic64_read() and atomic64_set() fall under "only > using the non-RMW operations of atomic_t"? But yes, I agree that any > locking is overkill. Yeah, I mean, it's an overkill. We can use seqlock or u64_stat here but it doesn't matter that much. > > > As for 64-bit on 32-bit machines -- that is a separate issue, but from > > > [1] it seems to me like there are more problems that *_ONCE() fixes than > > > just split reads and writes. > > > > Your explanations are too wishy washy. If you wanna fix it, please do > > it correctly. R/W ONCE isn't the right solution here. > > Sure, I will switch it to use atomic64_read() and atomic64_set() instead > if that's what you'd prefer. Though I will mention that on quite a few > architectures atomic64_read() is defined as: > > #define atomic64_read(v) READ_ONCE((v)->counter) Yeah, on archs which don't have split access on 64bits. On the ones which do, it does something else. The generic implementation is straight-up locking, I think. Thanks. -- tejun