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[2003:cb:c706:fd00:fb07:92f8:8f0c:6a08]) by smtp.gmail.com with ESMTPSA id n6-20020a05600c3b8600b0041892e839bcsm19431208wms.33.2024.04.23.01.18.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Apr 2024 01:18:25 -0700 (PDT) Message-ID: Date: Tue, 23 Apr 2024 10:18:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/rmap: remove unnecessary page_table_lock To: Yajun Deng , akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240422105212.1485788-1-yajun.deng@linux.dev> <3c452d5db5b3d5879160ab62a9e0ac4481a6298a@linux.dev> 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: <3c452d5db5b3d5879160ab62a9e0ac4481a6298a@linux.dev> 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-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 58A7840004 X-Rspam-User: X-Stat-Signature: a9667jjzqmq5dqpx8kobafysi3ow894e X-HE-Tag: 1713860309-271236 X-HE-Meta: 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 zFavRh9h 3pqQBJcO8/8WftzxS9N0cDlc0VAXa2ctJr6246XYV7+7NYfjmtKbfl/SBKpqbbKEjtnw/yk1rgFxHcv4MxMFmxRk2o4Zp7Ks3iYwJQnaOrnBmO764EcNond3OOqz7DG3/7eyyxEPP3uoV9vwAk1FNCzyK25iLdz2WrOlES4WvmGa8P27HlgjaIpBOUM3e/FVys2pd+1w9JQh0NEkALjw8Q7JcDDecDdvZba+D1CNzmz/ZoGwrKp7Mn27NvjApdQ0SCbVcZa98AZiCsXsRv1XtTd1dTyF4XRCyakbRNbqCkStKhbGTZ683kUa6qSLoeHBfHeR/+OVn5Eq40Tup9IwtwD7stbH0IScEsQ3PcogVfTYeng+Xn26GY6N1FZ/HianjWFdmpH+Nr4NoSQz3fih44onWqwbju0kBbZOrzx1l+u2mXSmV3fIGH6gtMQKkB2Xjvac+u82qa+5L7zmIWdv+hmUCOoWW4lSSCq8BLNPXXW/MRUU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.030639, 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 23.04.24 09:53, Yajun Deng wrote: > April 22, 2024 at 7:24 PM, "David Hildenbrand" wrote: > > > >> >> On 22.04.24 12:52, Yajun Deng wrote: >> >>> >>> page_table_lock is a lock that for page table, we won't change page >>> >>> table in __anon_vma_prepare(). As we can see, it works well in >>> >>> anon_vma_clone(). They do the same operation. >>> >> >> We are reusing mm->page_table_lock to serialize, not the *actual* low-level page table locks that really protect PTEs. >> >> With that locking gone, there would be nothing protection vma->anon_vma. >> >> Note that anon_vma_clone() is likely called with the mmap_lock held in write mode, which is not the case for __anon_vma_prepare() ... > > Yes, anon_vma_clone() is called with the mmap_lock held. I added mmap_assert_write_locked(dst->vm_mm) to prove it. > I added mmap_assert_write_locked(vma->vm_mm) in __anon_vma_prepare() at the same time, it shows __anon_vma_prepare() > is also called with the mmap_lock held too. Make sure you actually have lockdep built in and enabled. __anon_vma_prepare() is for example called from do_anonymous_page() where we might only hold the mmap_lock in read mode (or not at all IIRC with VMA in read mode). -- Cheers, David / dhildenb