From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 9C8EA7DC5B for ; Wed, 5 Dec 2018 09:20:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726102AbeLEJUO (ORCPT ); Wed, 5 Dec 2018 04:20:14 -0500 Received: from mail-ed1-f68.google.com ([209.85.208.68]:33215 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726861AbeLEJUN (ORCPT ); Wed, 5 Dec 2018 04:20:13 -0500 Received: by mail-ed1-f68.google.com with SMTP id p6so8110311eds.0 for ; Wed, 05 Dec 2018 01:20:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:reply-to:references:mime-version :content-disposition:in-reply-to:user-agent; bh=l3bYzngQOEI9Dy5+IQEyyY8JpQD1U2jOm8Ftqg4rJjM=; b=YX5UFlOgIgIIkBv+/rfK1KxHcU6sVWDv5Vdk0XwTaVQ6AZRH0u8a+YTywBBGJ8aFa4 rhy2X6gqauS1hJKJZ9RoYU3sw1gTMiBoTrtByMp/ngynpQhsJwEn7MEmDOa2nkwB2KUI RA1Uz4dyorEJIOvzHOuiV8z47VmXONG9929Ma07wTdbnZuaQCLeAozLZ7me80c7Mf7cO k9NTz6fWgDV1iLPQy9CNpWOR4UjE3q4sEReIQgyiXKTIqh1HNTpjs4saLGPo23Xz/gqD oAaOgIrt0h+9+Jrj7l/2sMJyRMZ7KRaz5iC7nQPm5lO+51TIWE6SjaLP5k2SOtS7hLA2 Rz6g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:reply-to :references:mime-version:content-disposition:in-reply-to:user-agent; bh=l3bYzngQOEI9Dy5+IQEyyY8JpQD1U2jOm8Ftqg4rJjM=; b=rHrjRtQkqhMnwsk6PcnjowP1EpZrKCDpy4dn0fLMRZIHayAeQmaQeMtXUxYO28KY+n PL3RWQOx/3YDeb3Myk8OGa/6QNhxK7c/yxfOk5oLFxBUUiGaYZ7DrpfWU7I4sEpRg6CT WlPKN1RummkGn9h7kpyIvF5iE+ki54VbJhurWA9cwHGOzJecyoWXUdZhQb9ApSTjCWsx a/tTf9ne84F7TYnt8Au0N/tODCFr91orobk+Sx4cwjgejsqdt37ELEUTNsFTkuUluTkp i/VY51ekqhMBrl9xa+6OdiOGUemaXwlSmweD9oreYO1FKkGnPUZaqetRXbLWqxm1nNwO h8dQ== X-Gm-Message-State: AA+aEWbPHs4B47Q+r+kkYlDhIaFY+Ca72FNv/+XACN8FZtrDWO/g5D1a UAsjebBuEZRwSCwATpq1qFI= X-Google-Smtp-Source: AFSGD/WA0OCJL5sI29YtI7OdV94ADiFNo7Q5xuVkYTv8lRzJ70H3/UhojtXsFauZbRSq6SI7kIgoeg== X-Received: by 2002:aa7:c248:: with SMTP id y8mr20274685edo.205.1544001610548; Wed, 05 Dec 2018 01:20:10 -0800 (PST) Received: from localhost ([185.92.221.13]) by smtp.gmail.com with ESMTPSA id x90sm5221523ede.35.2018.12.05.01.20.09 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 05 Dec 2018 01:20:09 -0800 (PST) Date: Wed, 5 Dec 2018 09:20:09 +0000 From: Wei Yang To: David Hildenbrand Cc: Wei Yang , mhocko@suse.com, osalvador@suse.de, akpm@linux-foundation.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, Jonathan Corbet , Mike Rapoport Subject: Re: [PATCH 1/2] admin-guide/memory-hotplug.rst: remove locking internal part from admin-guide Message-ID: <20181205092009.n5vb67bd6nuxwkcd@master> Reply-To: Wei Yang References: <20181205023426.24029-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, Dec 05, 2018 at 09:03:24AM +0100, David Hildenbrand wrote: >On 05.12.18 03:34, Wei Yang wrote: >> Locking Internal section exists in core-api documentation, which is more >> suitable for this. >> >> This patch removes the duplication part here. >> >> Signed-off-by: Wei Yang >> --- >> Documentation/admin-guide/mm/memory-hotplug.rst | 40 ------------------------- >> 1 file changed, 40 deletions(-) >> >> diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst >> index 5c4432c96c4b..241f4ce1e387 100644 >> --- a/Documentation/admin-guide/mm/memory-hotplug.rst >> +++ b/Documentation/admin-guide/mm/memory-hotplug.rst >> @@ -392,46 +392,6 @@ Need more implementation yet.... >> - Notification completion of remove works by OS to firmware. >> - Guard from remove if not yet. >> >> - >> -Locking Internals >> -================= >> - >> -When adding/removing memory that uses memory block devices (i.e. ordinary RAM), >> -the device_hotplug_lock should be held to: >> - >> -- synchronize against online/offline requests (e.g. via sysfs). This way, memory >> - block devices can only be accessed (.online/.state attributes) by user >> - space once memory has been fully added. And when removing memory, we >> - know nobody is in critical sections. >> -- synchronize against CPU hotplug and similar (e.g. relevant for ACPI and PPC) >> - >> -Especially, there is a possible lock inversion that is avoided using >> -device_hotplug_lock when adding memory and user space tries to online that >> -memory faster than expected: >> - >> -- device_online() will first take the device_lock(), followed by >> - mem_hotplug_lock >> -- add_memory_resource() will first take the mem_hotplug_lock, followed by >> - the device_lock() (while creating the devices, during bus_add_device()). >> - >> -As the device is visible to user space before taking the device_lock(), this >> -can result in a lock inversion. >> - >> -onlining/offlining of memory should be done via device_online()/ >> -device_offline() - to make sure it is properly synchronized to actions >> -via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type) >> - >> -When adding/removing/onlining/offlining memory or adding/removing >> -heterogeneous/device memory, we should always hold the mem_hotplug_lock in >> -write mode to serialise memory hotplug (e.g. access to global/zone >> -variables). >> - >> -In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read >> -mode allows for a quite efficient get_online_mems/put_online_mems >> -implementation, so code accessing memory can protect from that memory >> -vanishing. >> - >> - >> Future Work >> =========== >> >> > >I reported this yesterday to Jonathan and Mike > >https://lkml.org/lkml/2018/12/3/340 > Ah, Thanks :-) > >Anyhow > >Reviewed-by: David Hildenbrand > >-- > >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me