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[209.132.183.28]) by mx.google.com with ESMTPS id x190si3028788qkc.137.2019.05.16.00.10.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 16 May 2019 00:10:24 -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-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 740DDC004F44; Thu, 16 May 2019 07:10:22 +0000 (UTC) Received: from [10.36.117.24] (ovpn-117-24.ams2.redhat.com [10.36.117.24]) by smtp.corp.redhat.com (Postfix) with ESMTP id 41EE59894; Thu, 16 May 2019 07:10:13 +0000 (UTC) Subject: Re: [v5 0/3] "Hotremove" persistent memory To: Dan Williams , Pavel Tatashin Cc: "Verma, Vishal L" , "linux-kernel@vger.kernel.org" , "jmorris@namei.org" , "tiwai@suse.de" , "sashal@kernel.org" , "linux-mm@kvack.org" , "dave.hansen@linux.intel.com" , "bp@suse.de" , "akpm@linux-foundation.org" , "linux-nvdimm@lists.01.org" , "jglisse@redhat.com" , "zwisler@kernel.org" , "mhocko@suse.com" , "Jiang, Dave" , "bhelgaas@google.com" , "Busch, Keith" , "thomas.lendacky@amd.com" , "Huang, Ying" , "Wu, Fengguang" , "baiyaowei@cmss.chinamobile.com" References: <20190502184337.20538-1-pasha.tatashin@soleen.com> <76dfe7943f2a0ceaca73f5fd23e944dfdc0309d1.camel@intel.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 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Thu, 16 May 2019 07:10:23 +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 16.05.19 02:42, Dan Williams wrote: > On Wed, May 15, 2019 at 11:12 AM Pavel Tatashin > wrote: >> >>> Hi Pavel, >>> >>> I am working on adding this sort of a workflow into a new daxctl command >>> (daxctl-reconfigure-device)- this will allow changing the 'mode' of a >>> dax device to kmem, online the resulting memory, and with your patches, >>> also attempt to offline the memory, and change back to device-dax. >>> >>> In running with these patches, and testing the offlining part, I ran >>> into the following lockdep below. >>> >>> This is with just these three patches on top of -rc7. >>> >>> >>> [ +0.004886] ====================================================== >>> [ +0.001576] WARNING: possible circular locking dependency detected >>> [ +0.001506] 5.1.0-rc7+ #13 Tainted: G O >>> [ +0.000929] ------------------------------------------------------ >>> [ +0.000708] daxctl/22950 is trying to acquire lock: >>> [ +0.000548] 00000000f4d397f7 (kn->count#424){++++}, at: kernfs_remove_by_name_ns+0x40/0x80 >>> [ +0.000922] >>> but task is already holding lock: >>> [ +0.000657] 000000002aa52a9f (mem_sysfs_mutex){+.+.}, at: unregister_memory_section+0x22/0xa0 >> >> I have studied this issue, and now have a clear understanding why it >> happens, I am not yet sure how to fix it, so suggestions are welcomed >> :) > > I would think that ACPI hotplug would have a similar problem, but it does this: > > acpi_unbind_memory_blocks(info); > __remove_memory(nid, info->start_addr, info->length); > > I wonder if that ordering prevents going too deep into the > device_unregister() call stack that you highlighted below. > If that doesn't help, after we have [PATCH v2 0/8] mm/memory_hotplug: Factor out memory block device handling we could probably pull the memory device removal phase out from the mem_hotplug_lock protection and let it be protected by the device_hotplug_lock only. Might require some more work, though. -- Thanks, David / dhildenb