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b=eZzP/FiXpy188K8IQ2+WkQkpDUrAXFrBdIPhBTbbAGJwGwd9olZnyzdNkyUTgLWmh ek0iEnqgREe+LIp+akXe0NuCFYrp2PO47S5j9UmLAp0qYMnLrfuPOyMtkBpDhw2c0y 6U2EFSncINVVbDn3uLs6Wq8ExtSAJuA8BuQj/FBMOBYEuTdiLv0/hzQdERWOhijuEA NA79RbKR7u4PMZDkzIEbx6GJtQ1zADuLJ91DivfZ1k3AxxFnqOqF/tsKWOi+Pwfq4R mViyYNN2eCzTZ7maQmFciak7nJrz9p/WVydmyz+WfAzIbqyCES6HusgG2gs1SMDODs +OFceyZ926JqQ== Message-ID: <042c2846-c70b-415e-a3a5-0e69485d5c0b@kernel.org> Date: Wed, 7 Oct 2026 12:21:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/khugepaged: flush deferred unmaps before dropping a failed folio To: Kyle Zeng , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Zi Yan , Baolin Wang , outbounddisclosures@openai.com, stable@vger.kernel.org References: <20261007041001.43181-1-kylebot@openai.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: <20261007041001.43181-1-kylebot@openai.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 08661140004 X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: 4pbysono6oqg38c77yookmjnrn9tsxod X-HE-Tag: 1791368472-720561 X-HE-Meta: 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 5gxhrCM6 8LSzquhB3448pYBJYmmVLKu4s9ZJdHKt1euoD23R7ubYP1QZI+inWk7LWoH7xHghGda1rHyTTVZvpR2rA4ioFWUyBsyui56/Usp3tsTx2280nOxKTWzDGDrukHlvQRlJNGz9f8dYHX0qroURMLWYQF2PiFxX7WlAME6CgDXi2xiunDaXJ+e41LeDMTA4564ZnoCRM/bA88zkoouuOK8qpckoKTugUeY4Ajs2ROWq6o7Gbk73upeTV7JG7PGstofKWbm4O2CXPdMiMEFgfhSSyoIN8iPCXDSPNQTyOeKH6ydQllAM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/7/26 06:10, Kyle Zeng wrote: > collapse_file() can fail its reference-count or dirty-folio check after > unmapping with TTU_BATCH_FLUSH. Both paths put back the isolated folio, > then unlock it and drop the lookup reference before reaching the common > try_to_unmap_flush(). > > The page-cache reference does not keep the folio stable once the lock is > released. Another collapse can replace and free it. With its PTEs > already gone, that collapse cannot flush the first task's per-task TLB > batch, and retract_page_tables() skips short or unaligned VMAs. A CPU > can therefore retain a user translation to the freed folio. This has > been reproduced with unprivileged MADV_COLLAPSE on a memfd. > > Flush at out_unlock while the lookup reference and folio lock are still > held. The common flush continues to cover the accumulated pagelist on > both success and rollback, preserving batching on successful collapses. > > Fixes: 6d9df8a5889c ("mm/thp: collapse_file() do try_to_unmap(TTU_BATCH_FLUSH)") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Kyle Zeng > --- LGTM Acked-by: David Hildenbrand (Arm) -- Cheers, David