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b=sxrhJdMrDyvNGTo2+4rLETjfE3dSl3etSx39sar1MHn9UM3puwDLAAYVuFvnHHrj7 3K2ia82nNjfJ+0hf3CtQNK+C5QxJIyoeQGKobkC9Tsyev08aH6sYR1rTmpvFKB8+D9 aMpxVzuVTsnUHOuldO/nX13qdxjX7wIbTfmDvWiDX8kWzEzosKeXJCPSYVnQqDta07 o8JzYHMLIAI3YFxDJ5oevmZFojSd4UcKqKlEaQtKJ2gRdSfRfNEDbfkvegE9B0TXg0 kg93WwDpwOARQVfRsFiQ/9Zc6AcK5LKDaM3/HfdUyEH8TbsuBtqNIAh/ZPN0Lokul2 r8H7j0kY6N2kQ== Message-ID: <3e22afe6-ecf7-4180-9287-c48fea7b8be1@kernel.org> Date: Mon, 23 Feb 2026 10:23:11 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: A potential refcount issue during __folio_split To: Zi Yan , Wei Yang Cc: Linux MM References: <20260222010425.gbsjzhrew3pg4qrw@master> <20260222010708.uohpmddmzaa4i4ic@master> <6346656B-7518-4A55-8DEF-C2E975714C8B@nvidia.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <6346656B-7518-4A55-8DEF-C2E975714C8B@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: 3wrcjehfe6fekezcei3qphyca96sx7m3 X-Rspam-User: X-Rspamd-Queue-Id: E1A241C000D X-Rspamd-Server: rspam01 X-HE-Tag: 1771838595-619798 X-HE-Meta: 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 8Sz4ksGo D4CIRxsucJ90xFTe7L6LgoIdSIT3tjTrorlHfWzwqsTvpaCs1T/NdlAVB27d5bnhct0JWM3weS09SgE9PBNjJ7YCIekz9OVLn/qx6yrExh8f+kmaRKGjI2Fh9mGrLob91RoXkIs9uX9rLzzeOcrqWeCHJKsVDVwBLj3iMlX982VJlN31FbQfOhajnl1LRb9uCovC0Uj/4aiglJhruYeIvPfBk5H2+4yR00hLVp6gJAiEMCcWUdohHfSxe6IXGzUGiH6bE/YJX4YX+UWvpRmN6PSe/L8LRScwSCEjFYZC5d9/sn7pdDSYzImZ5Q3jNiLlZbOoZ+g4DLSSY8lZvkpGQ/u88BTk/xL2IDdY5B4D/EhuPbEg= 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: List-Subscribe: List-Unsubscribe: > BTW, in the folio world, I do not think it is possible to perform the aforementioned > split_huge_page_to_list_to_order() pattern any more, since you always work on folio, > the head. Unless there is a need of getting hold of a tail after-split folio after > a folio split, the pattern would be: > > tail_page = folio_page(folio, N); > > folio_get(folio); > folio_lock(folio); > folio_split(folio, ..., /* new parameter: lock_at = */ tail_page, ...); > tail_folio = page_folio(tail_page); > folio_unlock(tail_folio); > folio_put(tail_folio); Agreed. Maybe it would be even nicer if the split function could return the new folio directly. folio_get(folio); folio_lock(folio); split_folio = folio_split_XXX(folio, ..., tail_page, ...); if (IS_ERR_VALUE(split_folio)) { ... } folio_unlock(split_folio); folio_put(split__folio); -- Cheers, David