From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f199.google.com (mail-pl1-f199.google.com [209.85.214.199]) by kanga.kvack.org (Postfix) with ESMTP id B56AB6B771A for ; Wed, 5 Dec 2018 19:26:33 -0500 (EST) Received: by mail-pl1-f199.google.com with SMTP id h10so16036353plk.12 for ; Wed, 05 Dec 2018 16:26:33 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id az5sor29170747plb.11.2018.12.05.16.26.32 for (Google Transport Security); Wed, 05 Dec 2018 16:26:32 -0800 (PST) From: Wei Yang Subject: [PATCH v2 1/2] admin-guide/memory-hotplug.rst: remove locking internal part from admin-guide Date: Thu, 6 Dec 2018 08:26:21 +0800 Message-Id: <20181206002622.30675-1-richard.weiyang@gmail.com> In-Reply-To: <20181205023426.24029-1-richard.weiyang@gmail.com> References: <20181205023426.24029-1-richard.weiyang@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: rppt@linux.ibm.com, david@redhat.com, mhocko@suse.com, osalvador@suse.de Cc: akpm@linux-foundation.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, Wei Yang 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 Reviewed-by: David Hildenbrand Acked-by: Mike Rapoport --- 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 =========== -- 2.15.1