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[2003:cb:c706:4e00:31ad:5274:e21c:b59]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-428068cda0csm202163035e9.47.2024.07.30.02.58.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Jul 2024 02:58:32 -0700 (PDT) Message-ID: Date: Tue, 30 Jul 2024 11:58:31 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2] mm/gup: Clear the LRU flag of a page before adding to LRU batch To: Ge Yang , akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, 21cnbao@gmail.com, baolin.wang@linux.alibaba.com, liuzixing@hygon.cn References: <1719038884-1903-1-git-send-email-yangge1116@126.com> <3a2ab0ea-3a07-45a0-ae0e-b9d48bf409bd@redhat.com> <79234eac-d7cc-424b-984d-b78861a5e862@126.com> <9e018975-8a80-46a6-ab38-f3e2945c8878@redhat.com> <1c5f1582-d6ea-4e27-a966-e6e992cf7c22@126.com> <9f1b8c87-6ea4-4f88-9332-13ac4b1b35d9@126.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: <9f1b8c87-6ea4-4f88-9332-13ac4b1b35d9@126.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: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 97ED2C0023 X-Stat-Signature: nxptkosj7djwcka9enyifejtswax767p X-Rspam-User: X-HE-Tag: 1722333516-638690 X-HE-Meta: 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 iB7G9+oC B+OWXCUZa0n0fxNHvXzIZuZ248RKm61/j/Tr3X6LASxKTCsli9N75avk3LkAUo0IT7NpKpy5pDOfBuOLi/vuU30+9+E2FsstzplkpM1yFhaxL7Ax8qzIYEdUn6vJvCdUK8Qg/f7n5HWDwXtcUNeZqpfX0dWmcRHfE+VpPOJ5StkQujxdhjVpJS8xeG6Fa9DYhnGtCKej4FzJKzhvNOLRLJOk/9LNndtqQDIlontzh92XFshHjZ/4mv+NqEgEQ2IFZNPv+/zBRgo9KHg1ZW+214KzAYdK+yPOeAOCD2c5MMtqU1BlP1eKZeqbflbBAkgn2vwAvyL9gLRRs9PEfqyFws0s1BMAjXKy6CmYJ98VbD+4zpFqXdfeaaffINRzU3fH8TbP0kL7fvu1roBsZK/Wis8xs5zJbI1AJ+vbuksFuSD6EfTs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000153, 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 11:56, Ge Yang wrote: > > > 在 2024/7/30 17:41, David Hildenbrand 写道: >> On 30.07.24 11:36, Ge Yang wrote: >>> >>> >>> 在 2024/7/30 15:45, David Hildenbrand 写道: >>>>>> Looking at this in more detail, I wonder if we can turn that to >>>>>> >>>>>> if (!folio_test_clear_lru(folio)) >>>>>>        return; >>>>>> folio_get(folio); >>>>>> >>>>>> In all cases? The caller must hold a reference, so this should be >>>>>> fine. >>>>>> >>>>> >>>>> Seems the caller madvise_free_pte_range(...), calling >>>>> folio_mark_lazyfree(...), doesn't hold a reference on folio. >>>>> >>>> >>>> If that would be the case and the folio could get freed concurrently, >>>> the folio_get(folio) would be completely broken. >>>> >>>> In madvise_free_pte_range() we hold the PTL, so the folio cannot get >>>> freed concurrently. >>>> >>> >>> Right. >>> >>>> folio_get() is only allowed when we are sure the folio cannot get freed >>>> concurrently, because we know there is a reference that cannot go away. >>>> >>>> >>> >>> When cpu0 runs folio_activate(), and cpu1 runs folio_put() concurrently, >>> a possible bad scenario would like: >>> >>> cpu0                                           cpu1 >>> >>>                                              folio_put_testzero(folio) >>> if (!folio_test_clear_lru(folio))// Seems folio shouldn't be accessed >>> >>>          return; >>> folio_get(folio); >>>                                               __folio_put(folio) >>>                                               __folio_clear_lru(folio) >>> >>> >>> Seems we should use folio_try_get(folio) instead of folio_get(folio). >> >> In which case is folio_activate() called without the PTL on a mapped >> page or without a raised refcount? >> > > No such case has been found. But, folio_put() can be run at anytime, so > folio_activate() may access a folio with a reference count of 0. If you can't find such a case then nothing is broken and no switch to folio_try_get() is required. -- Cheers, David / dhildenb