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Mon, 24 Feb 2020 10:43:43 +0000 (UTC) Received: from [10.36.118.193] (unknown [10.36.118.193]) by smtp.corp.redhat.com (Postfix) with ESMTP id 499BD82063; Mon, 24 Feb 2020 10:43:37 +0000 (UTC) Subject: Re: [PATCH] mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled To: Vlastimil Babka , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Gerald Schaefer , Qian Cai , Joonsoo Kim , stable@vger.kernel.org References: <20200224094651.18257-1-vbabka@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: <48d481b7-3acd-3cf0-e27f-17755272df9e@redhat.com> Date: Mon, 24 Feb 2020 11:43:35 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200224094651.18257-1-vbabka@suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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 24.02.20 10:46, Vlastimil Babka wrote: > Commit cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC") fixed > memory hotplug with debug_pagealloc enabled, where onlining a page goes through > page freeing, which removes the direct mapping. Some arches don't like when the > page is not mapped in the first place, so generic_online_page() maps it first. > This is somewhat wasteful, but better than special casing page freeing fast > paths. > > The commit however missed that DEBUG_PAGEALLOC configured doesn't mean it's > actually enabled. One has to test debug_pagealloc_enabled() since 031bc5743f15 > ("mm/debug-pagealloc: make debug-pagealloc boottime configurable"), or alternatively > debug_pagealloc_enabled_static() since 8e57f8acbbd1 ("mm, debug_pagealloc: > don't rely on static keys too early"), but this is not done. > > As a result, a s390 kernel with DEBUG_PAGEALLOC configured but not enabled > will crash: > > Unable to handle kernel pointer dereference in virtual kernel address space > Failing address: 0000000000000000 TEID: 0000000000000483 > Fault in home space mode while using kernel ASCE. > AS:0000001ece13400b R2:000003fff7fd000b R3:000003fff7fcc007 S:000003fff7fd7000 P:000000000000013d > Oops: 0004 ilc:2 [#1] SMP > CPU: 1 PID: 26015 Comm: chmem Kdump: loaded Tainted: GX 5.3.18-5-default #1 SLE15-SP2 (unreleased) > Krnl PSW : 0704e00180000000 0000001ecd281b9e (__kernel_map_pages+0x166/0x188) > R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3 > Krnl GPRS: 0000000000000000 0000000000000800 0000400b00000000 0000000000000100 > 0000000000000001 0000000000000000 0000000000000002 0000000000000100 > 0000001ece139230 0000001ecdd98d40 0000400b00000100 0000000000000000 > 000003ffa17e4000 001fffe0114f7d08 0000001ecd4d93ea 001fffe0114f7b20 > Krnl Code: 0000001ecd281b8e: ec17ffff00d8 ahik %r1,%r7,-1 > 0000001ecd281b94: ec111dbc0355 risbg %r1,%r1,29,188,3 >> 0000001ecd281b9e: 94fb5006 ni 6(%r5),251 > 0000001ecd281ba2: 41505008 la %r5,8(%r5) > 0000001ecd281ba6: ec51fffc6064 cgrj %r5,%r1,6,1ecd281b9e > 0000001ecd281bac: 1a07 ar %r0,%r7 > 0000001ecd281bae: ec03ff584076 crj %r0,%r3,4,1ecd281a5e > Call Trace: > [<0000001ecd281b9e>] __kernel_map_pages+0x166/0x188 > [<0000001ecd4d9516>] online_pages_range+0xf6/0x128 > [<0000001ecd2a8186>] walk_system_ram_range+0x7e/0xd8 > [<0000001ecda28aae>] online_pages+0x2fe/0x3f0 > [<0000001ecd7d02a6>] memory_subsys_online+0x8e/0xc0 > [<0000001ecd7add42>] device_online+0x5a/0xc8 > [<0000001ecd7d0430>] state_store+0x88/0x118 > [<0000001ecd5b9f62>] kernfs_fop_write+0xc2/0x200 > [<0000001ecd5064b6>] vfs_write+0x176/0x1e0 > [<0000001ecd50676a>] ksys_write+0xa2/0x100 > [<0000001ecda315d4>] system_call+0xd8/0x2c8 > > Fix this by checking debug_pagealloc_enabled_static() before calling > kernel_map_pages(). Backports for kernel before 5.5 should use > debug_pagealloc_enabled() instead. Also add comments. > > Fixes: cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC") > Signed-off-by: Vlastimil Babka > Reported-by: Gerald Schaefer > Cc: Qian Cai > Cc: Joonsoo Kim > Cc: > --- > include/linux/mm.h | 4 ++++ > mm/memory_hotplug.c | 8 +++++++- > 2 files changed, 11 insertions(+), 1 deletion(-) > > diff --git include/linux/mm.h include/linux/mm.h > index 52269e56c514..c54fb96cb1e6 100644 > --- include/linux/mm.h > +++ include/linux/mm.h > @@ -2715,6 +2715,10 @@ static inline bool debug_pagealloc_enabled_static(void) > #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP) > extern void __kernel_map_pages(struct page *page, int numpages, int enable); > > +/* > + * When called in DEBUG_PAGEALLOC context, the call should most likely be > + * guarded by debug_pagealloc_enabled() or debug_pagealloc_enabled_static() > + */ > static inline void > kernel_map_pages(struct page *page, int numpages, int enable) > { > diff --git mm/memory_hotplug.c mm/memory_hotplug.c > index 0a54ffac8c68..19389cdc16a5 100644 > --- mm/memory_hotplug.c > +++ mm/memory_hotplug.c > @@ -574,7 +574,13 @@ EXPORT_SYMBOL_GPL(restore_online_page_callback); > > void generic_online_page(struct page *page, unsigned int order) > { > - kernel_map_pages(page, 1 << order, 1); > + /* > + * Freeing the page with debug_pagealloc enabled will try to unmap it, > + * so we should map it first. This is better than introducing a special > + * case in page freeing fast path. > + */ > + if (debug_pagealloc_enabled_static()) > + kernel_map_pages(page, 1 << order, 1); > __free_pages_core(page, order); > totalram_pages_add(1UL << order); > #ifdef CONFIG_HIGHMEM > Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb