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[2003:cb:c72a:9100:23d2:3800:cdcc:90f0]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3997f9e6450sm1951589f8f.70.2025.03.21.03.11.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Mar 2025 03:11:47 -0700 (PDT) Message-ID: <0d096764-302f-4b80-a867-22f5302b8045@redhat.com> Date: Fri, 21 Mar 2025 11:11:46 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] Fix parameter passed to page_mapcount_is_type() To: Vlastimil Babka , Gavin Shan , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, willy@infradead.org, osalvador@suse.de, gehao@kylinos.cn, shan.gavin@gmail.com References: <20250321053148.1434076-1-gshan@redhat.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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: EGxg5THNEJfJJ8yowCY61leV_C3CJmTOUguklco_G-Y_1742551909 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: rspam01 X-Stat-Signature: rd7o8ygfsmoejtc1bq7da7r6tiuoqoa1 X-Rspam-User: X-Rspamd-Queue-Id: 315AC40010 X-HE-Tag: 1742551913-482006 X-HE-Meta: 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 RlPoCYRE 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000443, 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 21.03.25 10:23, Vlastimil Babka wrote: > On 3/21/25 06:31, Gavin Shan wrote: >> Found by code inspection. There are two places where the parameter >> passed to page_mapcount_is_type() is (page->__mapcount), which is >> correct since it should be one more than the value, as explained in >> the comments to page_mapcount_is_type(): (a) page_has_type() in >> page-flags.h (b) __dump_folio() in mm/debug.c > > IIUC you are right. Luckily thanks to the the PGTY_mapcount_underflow limit, > this off-by-one error doesn't currently cause visible issues i.e. > misclassifications legitimate mapcount as page type and vice versa, right? > We'd have to have a mapcount underflown severely right to the limit to make > that off-by-one error cross it? Agreed. Likely not stable material because it isn't actually fixing anything (because of the safety gaps). > > I wonder if a more future-proof solution would be to redefine > page_mapcount_is_type() instead to not subtract. But I'll leave that to willy. With upcoming changes around that, likely best to leave that alone. I expect page_mapcount_is_type() to completely vanish. -- Cheers, David / dhildenb