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Wed, 24 Jun 2020 07:48:45 +0000 (UTC) Received: from [10.36.113.65] (ovpn-113-65.ams2.redhat.com [10.36.113.65]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1063A5BACC; Wed, 24 Jun 2020 07:48:43 +0000 (UTC) Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section To: Michal Hocko , Wei Yang Cc: akpm@linux-foundation.org, osalvador@suse.de, dan.j.williams@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20200623094258.6705-1-richard.weiyang@linux.alibaba.com> <20200623151828.GA31426@dhcp22.suse.cz> 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: <57d8a558-dcb3-b318-8e38-6c016b050414@redhat.com> Date: Wed, 24 Jun 2020 09:48:43 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200623151828.GA31426@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23.06.20 17:18, Michal Hocko wrote: > On Tue 23-06-20 17:42:58, Wei Yang wrote: >> For early sections, we assumes its memmap will never be partially >> removed. But current behavior breaks this. >> >> Let's correct it. >> >> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") >> Signed-off-by: Wei Yang > > Can a user trigger this or is this a theoretical bug? I tried to reproduce it, but somehow I get unexpected behavior. With a hacked QEMU I can get $ cat /proc/iomem [...] 100000000-143ffffff : System RAM 144000000-343dfffff : Persistent Memory 144000000-1441fffff : namespace0.0 144200000-144ffffff : dax0.0 After $ ndctl create-namespace --force --reconfig=namespace0.0 --mode=devdax --size=16M I get $ cat /proc/iomem [...] 100000000-143ffffff : System RAM 144000000-343dfffff : Persistent Memory 144000000-1441fffff : namespace0.0 144200000-144ffffff : dax0.0 I can trigger remove+re-add via $ ndctl create-namespace --force --reconfig=namespace0.0 --mode=devdax --size=16M So we clearly have an overlap between System RAM and dax0.0 within a section. However, I never get early_section() to trigger in section_activate()/section_deactivate() ? That's unexpected Definitely something seems to go wrong after the first "ndctl create-namespace". Using a random page walker: [root@localhost ~]# ./page-types [ 387.019229] general protection fault, probably for non-canonical address 0xfdfdfdfdfdfdfdfc: 0000 [#1] SMP NOPTI [ 387.020172] CPU: 17 PID: 1314 Comm: page-types Kdump: loaded Tainted: G W 5.8.0-rc2 #20 [ 387.021015] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.4 [ 387.022056] RIP: 0010:stable_page_flags+0x27/0x3f0 [ 387.022519] Code: 00 00 00 66 66 66 66 90 48 85 ff 0f 84 d2 03 00 00 41 54 55 48 89 fd 53 48 8b 57 08 48 8b 1f 48f [ 387.024291] RSP: 0018:ffff9f8781057e58 EFLAGS: 00010202 [ 387.024775] RAX: fdfdfdfdfdfdfdfc RBX: fdfdfdfdfdfdfdfd RCX: 00007ffc4f4f1f78 [ 387.025423] RDX: 0000000000000001 RSI: 0000002000000000 RDI: ffffc590c5100000 [ 387.026052] RBP: ffffc590c5100000 R08: 0000000000000001 R09: 0000000000000000 [ 387.026696] R10: 0000000000000000 R11: 0000000000000000 R12: 00007ffc4f4f1f80 [ 387.027324] R13: 0000000000040000 R14: 00007ffc4f4d1f80 R15: ffffffffa1577ee0 [ 387.027974] FS: 00007f91a0f9c580(0000) GS:ffff888b3f7c0000(0000) knlGS:0000000000000000 [ 387.028699] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 387.029223] CR2: 0000000000449b00 CR3: 000000007a7fc000 CR4: 00000000000006e0 [ 387.029864] Call Trace: [ 387.030108] kpageflags_read+0xcc/0x160 [ 387.030473] proc_reg_read+0x53/0x80 [ 387.030809] vfs_read+0x9d/0x150 [ 387.031114] ksys_pread64+0x65/0xa0 [ 387.031449] do_syscall_64+0x4d/0x90 [ 387.031783] entry_SYSCALL_64_after_hwframe+0x44/0xa9 -- Thanks, David / dhildenb