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=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 09B79C2D0DB for ; Fri, 24 Jan 2020 13:48:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C755622464 for ; Fri, 24 Jan 2020 13:48:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="d/YiwtWd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390011AbgAXNsa (ORCPT ); Fri, 24 Jan 2020 08:48:30 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:38719 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2387592AbgAXNsa (ORCPT ); Fri, 24 Jan 2020 08:48:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579873708; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=KvmhSDHhrMTdDP9Vr2OkCvFf0wdB6GMHex83pKYYzbc=; b=d/YiwtWdmEmFa7Ay596bBaS8MQOiLzj2CLdn0LYE9she3Lys8FyhtotzJSlmzzmmQU/3d3 tv1he687PL6ZJI2lHj5IFA34LATBNJYEJ84LR6h2jkpjJCnZFYbmgWiW3ARgYpn6q00W0i CDjFblEhQplvSaUTwTKQ1DKkSkctddY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-132-qfhxiFrkM9aogSsvuSLWSg-1; Fri, 24 Jan 2020 08:48:24 -0500 X-MC-Unique: qfhxiFrkM9aogSsvuSLWSg-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id BE6F38010C5; Fri, 24 Jan 2020 13:48:22 +0000 (UTC) Received: from [10.36.116.39] (ovpn-116-39.ams2.redhat.com [10.36.116.39]) by smtp.corp.redhat.com (Postfix) with ESMTP id BC84D60BEC; Fri, 24 Jan 2020 13:48:20 +0000 (UTC) Subject: Re: [PATCH v1] driver core: check for dead devices before onlining/offlining From: David Hildenbrand To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, "Rafael J. Wysocki" , Suzuki K Poulose , Saravana Kannan , Heikki Krogerus , Dan Williams , Michal Hocko References: <20200120104909.13991-1-david@redhat.com> <20200124090052.GA2958140@kroah.com> <6dd0ea5a-e5c3-c4b6-2b2e-93537571d7d6@redhat.com> <20200124091221.GA2983380@kroah.com> Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: Date: Fri, 24 Jan 2020 14:48:19 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24.01.20 14:31, David Hildenbrand wrote: > On 24.01.20 10:12, Greg Kroah-Hartman wrote: >> On Fri, Jan 24, 2020 at 10:09:03AM +0100, David Hildenbrand wrote: >>> On 24.01.20 10:00, Greg Kroah-Hartman wrote: >>>> On Mon, Jan 20, 2020 at 11:49:09AM +0100, David Hildenbrand wrote: >>>>> We can have rare cases where the removal of a device races with >>>>> somebody trying to online it (esp. via sysfs). We can simply check >>>>> if the device is already removed or getting removed under the dev->lock. >>>>> >>>>> E.g., right now, if memory block devices are removed (remove_memory()), >>>>> we do a: >>>>> >>>>> remove_memory() -> lock_device_hotplug() -> mem_hotplug_begin() -> >>>>> lock_device() -> dev->dead = true >>>>> >>>>> Somebody coming via sysfs (/sys/devices/system/memory/memoryX/online) >>>>> triggers a: >>>>> >>>>> lock_device_hotplug_sysfs() -> device_online() -> lock_device() ... >>>>> >>>>> So if we made it just before the lock_device_hotplug_sysfs() but get >>>>> delayed until remove_memory() released all locks, we will continue >>>>> taking locks and trying to online the device - which is then a zombie >>>>> device. >>>>> >>>>> Note that at least the memory onlining path seems to be protected by >>>>> checking if all memory sections are still present (something we can then >>>>> get rid of). We do have other sysfs attributes >>>>> (e.g., /sys/devices/system/memory/memoryX/valid_zones) that don't do any >>>>> such locking yet and might race with memory removal in a similar way. For >>>>> these users, we can then do a >>>>> >>>>> device_lock(dev); >>>>> if (!device_is_dead(dev)) { >>>>> /* magic /* >>>>> } >>>>> device_unlock(dev); >>>>> >>>>> Introduce and use device_is_dead() right away. >>>>> >>>>> Cc: Greg Kroah-Hartman >>>>> Cc: "Rafael J. Wysocki" >>>>> Cc: Suzuki K Poulose >>>>> Cc: Saravana Kannan >>>>> Cc: Heikki Krogerus >>>>> Cc: Dan Williams >>>>> Cc: Michal Hocko >>>>> Signed-off-by: David Hildenbrand >>>>> --- >>>>> >>>>> Am I missing any obvious mechanism in the device core that handles >>>>> something like this already? (especially also for other sysfs attributes?) >>>> >>>> So is a sysfs attribute causing the device itself to go away? We have >>> >>> nope, removal is triggered via the driver, not via a sysfs attribute. >> >> But the idea is the same, it comes from the driver, not the driver core. >> >>> Regarding this patch: Is there anything prohibiting the possible >>> scenario I document above (IOW, is this patch applicable, or is there >>> another way to fence it properly (e.g., the "specific call" you mentioned))? >> >> I think it's the same thing, look at how scsi does it. > > I think you are talking about doing a "transport_remove_device(dev)" > before doing the "device_del(dev)", combined with proper locking. > > Will look into that for the memory subsystem ... ... looking into transports, it most probably does not apply here, hmm ... -- Thanks, David / dhildenb