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[209.132.183.28]) by mx.google.com with ESMTPS id y24si1802842qkj.218.2019.04.25.05.38.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 25 Apr 2019 05:38:29 -0700 (PDT) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B21B83099FCA; Thu, 25 Apr 2019 12:38:26 +0000 (UTC) Received: from [10.36.116.47] (ovpn-116-47.ams2.redhat.com [10.36.116.47]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1EA9560C99; Thu, 25 Apr 2019 12:38:21 +0000 (UTC) Subject: Re: [v2 2/2] device-dax: "Hotremove" persistent memory that is used like normal RAM To: Pavel Tatashin Cc: Dan Williams , James Morris , Sasha Levin , Linux Kernel Mailing List , Linux MM , linux-nvdimm , Andrew Morton , Michal Hocko , Dave Hansen , Keith Busch , Vishal L Verma , Dave Jiang , Ross Zwisler , Tom Lendacky , "Huang, Ying" , Fengguang Wu , Borislav Petkov , Bjorn Helgaas , Yaowei Bai , Takashi Iwai , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= References: <20190421014429.31206-1-pasha.tatashin@soleen.com> <20190421014429.31206-3-pasha.tatashin@soleen.com> <4ad3c587-6ab8-1307-5a13-a3e73cf569a5@redhat.com> <180d6250-8a6a-0b5d-642a-ec6648cb45b1@redhat.com> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Thu, 25 Apr 2019 12:38:29 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 25.04.19 14:30, Pavel Tatashin wrote: >> >> Yes, also I think you can let go of the device_lock in >> check_memblocks_offline_cb, lock_device_hotplug() should take care of >> this (see Documentation/core-api/memory-hotplug.rst - "locking internals") >> > Hi David, > > Thank you for your comments. I went through memory-hotplug.rst, and I > still think that device_lock() is needed here. In this particular case > it can be replaced with something like READ_ONCE(), but for simplicity > it is better to have device_lock()/device_unlock() as this is not a > performance critical code. > > I do not see any lock ordering issues with this code, as we are > holding lock_device_hotplug() first that prevents userland from > adding/removing memory during this check. Yes, lock ordering is not an issue, I rather think that the device hotplug lock will guard us in all situations. E.g. remove_memory() also does not use it when checking if all blocks are offline. But you can leave it in if you think it is needed. > > https://soleen.com/source/xref/linux/arch/powerpc/platforms/powernv/memtrace.c?r=98fa15f3#248 > > Here we have a similar code: > lock_device_hotplug(); > online_mem_block(); > device_online() > device_lock(dev); > > Pasha > -- Thanks, David / dhildenb