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=-10.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 0FADCC43603 for ; Fri, 20 Dec 2019 10:51:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B15C024680 for ; Fri, 20 Dec 2019 10:51:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Us2NFAjQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727359AbfLTKvE (ORCPT ); Fri, 20 Dec 2019 05:51:04 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:56869 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726210AbfLTKvE (ORCPT ); Fri, 20 Dec 2019 05:51:04 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1576839062; 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=fluIzYbR26a/yPgpK/E4xZ/RCtwo0lThgvVAxHbP8+w=; b=Us2NFAjQGuNE/+wokPZG4lBfPjt8qw7AWUkugndCvY9xAYwRf68rwxZCTeL+pFbtjozUik Y+3wp+O8FMYBiFIkjy1Ic6e7lYDmNdyHYD9M6h2w+x1ckwygLL0JeSX3Pwze/xEsFM7Eve PgIATTtTyxXUopQ6/DlFpdn2DDa9sMs= 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-322-QZz8uAntNTiuVLTbXERsVA-1; Fri, 20 Dec 2019 05:50:59 -0500 X-MC-Unique: QZz8uAntNTiuVLTbXERsVA-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 B2EBF100550E; Fri, 20 Dec 2019 10:50:57 +0000 (UTC) Received: from [10.36.117.63] (ovpn-117-63.ams2.redhat.com [10.36.117.63]) by smtp.corp.redhat.com (Postfix) with ESMTP id C04B460BEC; Fri, 20 Dec 2019 10:50:55 +0000 (UTC) Subject: Re: [PATCH v3] drivers/base/memory.c: cache blocks in radix tree to accelerate lookup To: Scott Cheloha Cc: linux-kernel@vger.kernel.org, "Rafael J. Wysocki" , Greg Kroah-Hartman , Michal Hocko , Oscar Salvador , "akpm@linux-foundation.org" References: <20191121195952.3728-1-cheloha@linux.vnet.ibm.com> <20191217193238.3098-1-cheloha@linux.vnet.ibm.com> <20191219173336.v6uvlu4gqz26gvmm@rascal.austin.ibm.com> From: David Hildenbrand 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, 20 Dec 2019 11:50:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <20191219173336.v6uvlu4gqz26gvmm@rascal.austin.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19.12.19 18:33, Scott Cheloha wrote: > On Wed, Dec 18, 2019 at 10:00:49AM +0100, David Hildenbrand wrote: >> On 17.12.19 20:32, Scott Cheloha wrote: >>> Searching for a particular memory block by id is slow because each bl= ock >>> device is kept in an unsorted linked list on the subsystem bus. >>> >>> Lookup is much faster if we cache the blocks in a radix tree. Memory >>> subsystem initialization and hotplug/hotunplug is at least a little f= aster >>> for any machine with more than ~100 blocks, and the speedup grows wit= h >>> the block count. >>> >>> Signed-off-by: Scott Cheloha >>> Acked-by: David Hildenbrand >>> --- >>> v2 incorporates suggestions from David Hildenbrand. >>> >>> v3 changes: >>> - Rebase atop "drivers/base/memory.c: drop the mem_sysfs_mutex" >>> >>> - Be conservative: don't use radix_tree_for_each_slot() in >>> walk_memory_blocks() yet. It introduces RCU which could >>> change behavior. Walking the tree "by hand" with >>> find_memory_block_by_id() is slower but keeps the patch >>> simple. >> >> Fine with me (splitting it out, e.g., into an addon patch), however, a= s >> readers/writers run mutually exclusive, there is nothing to worry abou= t >> here. RCU will not make a difference. >=20 > Oh. In that case, can you make heads or tails of this CI failure > email I got about the v2 patch? I've inlined it at the end of this > mail. "Suspicious RCU usage". Unclear if it's a false positive. My > thinking was that I'd hold off on using radix_tree_for_each_slot() and > introducing a possible regression until I understood what was > triggering the robot. Ah, did not see that message. See below. >=20 > Also, is there anyone else I should shop this patch to? I copied the > maintainers reported by scripts/get_maintainer.pl but are there others > who might be interested? On memory hotplug (and related) things, it's usually a good idea to CC Andrew (who picks up basically all MM stuff), Michal Hocko, and Oscar Salvador. (cc-ing them) >=20 > -- >=20 > Here's that CI mail. I've stripped the attached config because it's > huge. >=20 > Date: Sun, 1 Dec 2019 23:05:23 +0800 > From: kernel test robot > To: Scott Cheloha > Cc: 0day robot , LKP > Subject: 86dc301f7b ("drivers/base/memory.c: cache blocks in radix tree= .."): > [ 1.341517] WARNING: suspicious RCU usage > Message-ID: <20191201150523.GE18573@shao2-debian> >=20 > Greetings, >=20 > 0day kernel testing robot got the below dmesg and the first bad commit = is >=20 > https://github.com/0day-ci/linux/commits/Scott-Cheloha/drivers-base-mem= ory-c-cache-blocks-in-radix-tree-to-accelerate-lookup/20191124-104557 >=20 > commit 86dc301f7b4815d90e3a7843ffed655d64efe445 > Author: Scott Cheloha > AuthorDate: Thu Nov 21 13:59:52 2019 -0600 > Commit: 0day robot > CommitDate: Sun Nov 24 10:45:59 2019 +0800 >=20 > drivers/base/memory.c: cache blocks in radix tree to accelerate loo= kup > =20 > Searching for a particular memory block by id is slow because each = block > device is kept in an unsorted linked list on the subsystem bus. > =20 > Lookup is much faster if we cache the blocks in a radix tree. Memo= ry > subsystem initialization and hotplug/hotunplug is at least a little= faster > for any machine with more than ~100 blocks, and the speedup grows w= ith > the block count. > =20 > Signed-off-by: Scott Cheloha > Acked-by: David Hildenbrand >=20 > 0e4a459f56 tracing: Remove unnecessary DEBUG_FS dependency > 86dc301f7b drivers/base/memory.c: cache blocks in radix tree to accele= rate lookup > +---------------------------------------------------------------------+= ------------+------------+ > | |= 0e4a459f56 | 86dc301f7b | > +---------------------------------------------------------------------+= ------------+------------+ > | boot_successes |= 8 | 0 | > | boot_failures |= 25 | 11 | > | WARNING:possible_circular_locking_dependency_detected |= 25 | 8 | > | WARNING:suspicious_RCU_usage |= 0 | 11 | > | include/linux/radix-tree.h:#suspicious_rcu_dereference_check()usage |= 0 | 11 | > +---------------------------------------------------------------------+= ------------+------------+ >=20 > If you fix the issue, kindly add following tag > Reported-by: kernel test robot >=20 > [ 1.335279] random: get_random_bytes called from kcmp_cookies_init+0= x29/0x4c with crng_init=3D0 > [ 1.336883] ACPI: bus type PCI registered > [ 1.338295] PCI: Using configuration type 1 for base access > [ 1.340735]=20 > [ 1.341049] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > [ 1.341517] WARNING: suspicious RCU usage > [ 1.342266] 5.4.0-rc5-00070-g86dc301f7b481 #1 Tainted: G = T > [ 1.343494] ----------------------------- > [ 1.344226] include/linux/radix-tree.h:167 suspicious rcu_dereferenc= e_check() usage! > [ 1.345516]=20 > [ 1.345516] other info that might help us debug this: > [ 1.345516]=20 > [ 1.346962]=20 > [ 1.346962] rcu_scheduler_active =3D 2, debug_locks =3D 1 > [ 1.348134] no locks held by swapper/0/1. > [ 1.348866]=20 > [ 1.348866] stack backtrace: > [ 1.349525] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G = T 5.4.0-rc5-00070-g86dc301f7b481 #1 > [ 1.351230] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), B= IOS 1.10.2-1 04/01/2014 > [ 1.352720] Call Trace: > [ 1.353187] ? dump_stack+0x9a/0xde > [ 1.353507] ? node_access_release+0x19/0x19 > [ 1.353507] ? walk_memory_blocks+0xe6/0x184 > [ 1.353507] ? set_debug_rodata+0x20/0x20 > [ 1.353507] ? link_mem_sections+0x39/0x3d > [ 1.353507] ? topology_init+0x74/0xc8 > [ 1.353507] ? enable_cpu0_hotplug+0x15/0x15 > [ 1.353507] ? do_one_initcall+0x13d/0x30a > [ 1.353507] ? kernel_init_freeable+0x18e/0x23b > [ 1.353507] ? rest_init+0x173/0x173 > [ 1.353507] ? kernel_init+0x10/0x151 > [ 1.353507] ? rest_init+0x173/0x173 > [ 1.353507] ? ret_from_fork+0x3a/0x50 > [ 1.410829] HugeTLB registered 2.00 MiB page size, pre-allocated 0 p= ages > [ 1.427389] cryptd: max_cpu_qlen set to 1000 > [ 1.457792] ACPI: Added _OSI(Module Device) > [ 1.458615] ACPI: Added _OSI(Processor Device) > [ 1.459428] ACPI: Added _OSI(3.0 _SCP Extensions) >=20 We get a complaint that we do a rcu_dereference() without proper protecti= on. We come via rest_init()->kernel_init()->kernel_init_freeable()->do_basic_setup()-> do_initcalls()->do_initcall_level()->do_one_initcall()-> topology_init()->register_one_node()->link_mem_sections()-> walk_memory_blocks() E.g., we add ACPI memory similarly via ...do_initcalls()...acpi_init()->acpi_scan_init() also without holding the device hotplug lock. AFAIK, we can't get races/concurrent hot(un)plug activity here (we even documented that for ACPI). And if we would, the code would already be wrong ;) I assume the simplest and cheapest way to suppress the warning would be to add rcu_read_lock()/rcu_read_unlock() around the radix_tree_for_each_slot(). Another way to suppress the warning would be to take the device hotplug lock before calling register_one_node() in all arch specific code - but we had a similar discussion due to the ACPI code back then and decided to not take the device hotplug lock if not really necessary. ... but after all we would want a radix_tree_for_each_slot() variant that does not perform such checks here. We don't hold any locks and don't need any locks. --=20 Thanks, David / dhildenb