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 A4B0BFA372A for ; Wed, 16 Oct 2019 14:28:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E38821848 for ; Wed, 16 Oct 2019 14:28:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571236083; bh=a/0Mo+yQV9Rtw2SL/6iBHZjhh3OlOHHqnfsKkqcVhJA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=Q6w8NS4/dKSRI8dPKaauNK0XQKASgh1cyhuZje6rabxZ4PzLaN277VWFSQ73R1Zjv fr5ppsmbUAEhXf0nQmYFHlcftX487J7pIaUDikrkT4EETHtApOnsFGhj1O8p292kze HSmlrDosPAcsJdoAvOj43Yx4PLl/8OY9yWR0C8Ts= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394058AbfJPO2C (ORCPT ); Wed, 16 Oct 2019 10:28:02 -0400 Received: from mail-qk1-f195.google.com ([209.85.222.195]:36187 "EHLO mail-qk1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728559AbfJPO2C (ORCPT ); Wed, 16 Oct 2019 10:28:02 -0400 Received: by mail-qk1-f195.google.com with SMTP id y189so22940535qkc.3; Wed, 16 Oct 2019 07:28:01 -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=pWLBPoWyBcOr16gWtiZJvZNkZ+CpdbY6LbEquS4WgGs=; b=SWezzmlqWZweUFaF4bfjHi2Tkkw8IwVCxK4pMU0MbQZvbR2h4E82Y8SaKq2ezH2umM WfPRhFIQakPbA8Otm9Wuc/6yBmHY4iHer+p4UI/OZl4/gWanrHa4EIwbFby9zsvbYmst sWi85/Xa/YV9FyaWVkBgxd8vgS0+SgZgr1wypsV68+Tu6PJ9AimgXsQ0fRyR3xx73Q7/ VQ/IVepjPClxC2g2duudYJbd/4GD7ExOPqSKzsrX/nP38Q/ZBh6/JL0z+o5sg5Qz/npy zyNO86sjKko2KZdlxldTUeds1q9AfwACNfH60szRWGnZJwbBwXGDTDGCU2n/HhUGYXR/ zDTQ== 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=pWLBPoWyBcOr16gWtiZJvZNkZ+CpdbY6LbEquS4WgGs=; b=Q84H98xY79oTc8lUrYgc8V83YBeberotMMqhmkPaxDzfJEHh0TfYEVFf3G+fzX3QM5 35HnAsrVyF/qd5B3+EMU3K2+0MF5RWiKJrTnZpb5IeM/CXzKzZJJs5UMOpVcvLhAkGH0 354zO0RwxsERQ67AvOBElJotyFQJkrfbGUmbAWlvnL30stg7KFj3Fw2y22HxcM2sIGqp b8VlOMm/BLLxSgRDc9MxzXLYmj+djFlXIWiMzluPtybowPnEsmWmxthHcDdPknUusUSz 0bzxHJ9R9Uw+wszyfxvDMDE0tjah7Y64Kmjxw8d6G8lAi7hPJtwi3fUnKZpugruVMaeS 0sZQ== X-Gm-Message-State: APjAAAVoIgtgU8T8U3zXCmONFhH+EioT0r/jii6keZtBQKg8G0Reuhgy 05lT5GS7gaF0qA53uExCEvg= X-Google-Smtp-Source: APXvYqz36gDcDPyEKnQuRJpODNwdYI7/eHC6toKsYq0xzoKu6JG9Ve4tnsU7B/Lb3kB7hGC2V8yaRw== X-Received: by 2002:a37:68a:: with SMTP id 132mr3949742qkg.359.1571236080574; Wed, 16 Oct 2019 07:28:00 -0700 (PDT) Received: from localhost ([2620:10d:c091:500::1:2d57]) by smtp.gmail.com with ESMTPSA id g194sm12328186qke.46.2019.10.16.07.27.59 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 16 Oct 2019 07:27:59 -0700 (PDT) Date: Wed, 16 Oct 2019 07:27:56 -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: <20191016142756.GN18794@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191016083218.ttsaqnxpjh5i5bgv@yavin.dot.cyphar.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Aleksa. On Wed, Oct 16, 2019 at 07:32:19PM +1100, Aleksa Sarai wrote: > Maybe I'm misunderstanding Documentation/atomic_t.txt, but it looks to > me like it's explicitly saying that I shouldn't use atomic64_t if I'm > just using it for fetching and assignment. Hah, where is it saying that? The alternative would be seqlock or u64_stats or straight-up locking but idk for this atomic64_t should be fine. > > The non-RMW ops are (typically) regular LOADs and STOREs and are > > canonically implemented using READ_ONCE(), WRITE_ONCE(), > > smp_load_acquire() and smp_store_release() respectively. 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. > > 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. Thanks. -- tejun