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[2003:cb:c706:4e00:31ad:5274:e21c:b59]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-428265289bdsm14630115e9.17.2024.07.30.08.45.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Jul 2024 08:45:25 -0700 (PDT) Message-ID: Date: Tue, 30 Jul 2024 17:45:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] mm: let pte_lockptr() consume a pte_t pointer To: Marek Szyprowski , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Muchun Song , Peter Xu , Oscar Salvador References: <20240725183955.2268884-1-david@redhat.com> <20240725183955.2268884-2-david@redhat.com> <97d87df8-6076-4df0-90a9-a8f5ddea42e9@samsung.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <97d87df8-6076-4df0-90a9-a8f5ddea42e9@samsung.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: zgbiacwao3p9fdokmtf5mtr9a949w566 X-Rspamd-Queue-Id: EF560C0029 X-Rspamd-Server: rspam11 X-HE-Tag: 1722354330-150403 X-HE-Meta: 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 O8GWGSJE Q29yxLSTmMcq7iDiTkSCkK9r02xPApx/wY6UEd1J8us5O6I1+ZP6Q4HvMuXYmEieRwNJ+iY7ArcLHGh555Llg8q0mGXCSoyhFUXd34P6k4TjEE8EIHAmymVs3Cd/6XGW3cIFVa9lTmSEVsA0/o6rLLjfIYwWgQ66zdFFrK3NCQJ+YNuz3TOtGbbJmJpgD1jEwVWNQOKLXdzRBRmBC25VKv0HzzRmOrKVS91v9fCTogOC5hW+e4q9XcjZVEkenZxbzMpyq2Gl6YFiYcs7mXvfN+zQZ9Zgcdi2ue4LLrZzzju7KtBJ8/Xb8ewOovj6vrlKAB1oQBiD+oG+rRxK4TKv7KcP2soEc1Jg9VYFHni5RXcWDJCWh0YPyAd+qF3L0V/A4ZvGqPhwJ3mSBMz2d0QIQO+Y9JSK1L1A5YgCxFh8OI8h0XlALHsClL9RgdrmSgx4Xhv6T X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 30.07.24 17:30, Marek Szyprowski wrote: > On 25.07.2024 20:39, David Hildenbrand wrote: >> pte_lockptr() is the only *_lockptr() function that doesn't consume >> what would be expected: it consumes a pmd_t pointer instead of a pte_t >> pointer. >> >> Let's change that. The two callers in pgtable-generic.c are easily >> adjusted. Adjust khugepaged.c:retract_page_tables() to simply do a >> pte_offset_map_nolock() to obtain the lock, even though we won't actually >> be traversing the page table. >> >> This makes the code more similar to the other variants and avoids other >> hacks to make the new pte_lockptr() version happy. pte_lockptr() users >> reside now only in pgtable-generic.c. >> >> Maybe, using pte_offset_map_nolock() is the right thing to do because >> the PTE table could have been removed in the meantime? At least it sounds >> more future proof if we ever have other means of page table reclaim. >> >> It's not quite clear if holding the PTE table lock is really required: >> what if someone else obtains the lock just after we unlock it? But we'll >> leave that as is for now, maybe there are good reasons. >> >> This is a preparation for adapting hugetlb page table locking logic to >> take the same locks as core-mm page table walkers would. >> >> Signed-off-by: David Hildenbrand > > This patch landed in today's linux-next as commit e98970a1d2d4 ("mm: let > pte_lockptr() consume a pte_t pointer"). Unfortunately it causes the > following issue on most of my ARM 32bit based test boards: > That is ... rather surprising. The issue below seems to point at __pte_offset_map_lock(), where we essentially convert from ptlock_ptr(page_ptdesc(pmd_page(*pmd))); to ptlock_ptr(virt_to_ptdesc(pte)); So we would get a NULL ptr from the ptdesc. Either the lock would actually not be allocated or virt_to_ptdesc() does something unexpected. Leaf page tables on arm are also a single page, so we cannot possibly be staring at the wrong page-table-subpage. Do we maybe have to special-case init-mm? But I don't see how that special-casing would have happened for now :/ What's your kernel config value of SPLIT_PTLOCK_CPUS? -- Cheers, David / dhildenb