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b=ClavKX2Yh5C1NgfFlXnAGS9n2b7ylvpH2CPkf+F7/BcQWTKgLxoCWVWDgOL5edYb5 60xjfocL0vskCdqhPyyZLRLTjkELQ+RSaP83s06muJYb5CX6PFh1Qr2qr8l5rHgdC0 9wrx3/cmczbtxRoI5n4rOU/OMLNadMngtO9Mn6OyfCTsVeSPOFU7ADNnN9oCvCzeB+ rzhu9aJKSVVkaEVX8Z2CGUAGFGGmup2j9BjGWBGmoirsKCrysLpnTaXRcINJKtGf13 0F/5nDU00m2YnBy+oq+oH945efjM9sTQzQrkP7PaoAWzOKnfvV/Q/89hvr1YS6kT0D UMiCPFHhm7yrA== Message-ID: Date: Wed, 7 Oct 2026 12:58:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/gup: document unlocked invariant in fixup_user_fault To: =?UTF-8?B?Tmjhuq10IEFuaCBOZ3V54buFbiBEdXk=?= Cc: akpm@linux-foundation.org, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261004125601.c06953a6f0660df9859b0c2a@linux-foundation.org> <20261005093756.22709-1-neganhat@gmail.com> <645204ff-6c50-4ef3-9070-78ac602560b1@kernel.org> 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: E71AC20002 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: mzhjf6rykw14m9dp71gu4rca3cz796d1 X-HE-Tag: 1791370713-228055 X-HE-Meta: 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 UjMr3YV8 qiRsWP657GIAE1UL3E0zte+12mAIvtSIONwTIoIUVKnC49eY8PIcBNUAXJxjQ9KjSqvBZfEksUWaIvbo0prTkpF/+02TRFUVD5ilGTe9BpkP1N4R0De7/ImkgDCmEskAff3ejZNZFooPE2aaFNib7+tCsK063whmwbN7JJzXP5fstrwKDhXMp8zv75h4EK/UZRywGnk+fa0oXHB0i/SeDZHh+A3HJLfZmXmnCJVRaDaO19OA+Q5vPEWISjZsWR7RvQsLg7Vm3yOCF/uPJrKlSkCT7dqP07S7VTTFb35+yCscsD2J/mPGRTcL+H6uwZOrCSCftH/4xl68uvDQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/5/26 13:22, Nhật Anh Nguyễn Duy wrote: > Hi David, > Hi, > Thanks for taking the time to review. > > My motivation came from running Smatch over fixup_user_fault(), which flagged just like the (at least) 2 previous reports. One from them from 2021 IIRC where Linus even rejected a code change. > the dereference as a potential NULL pointer issue. Because the relationship > between FAULT_FLAG_ALLOW_RETRY and the unlocked pointer is subtle when > first reading through the path, I initially misread it as an unguarded > dereference in v1. > > When Andrew pointed out the invariant, I thought documenting it might help > future readers or newer contributors who hit the same static analysis warning. > > If adding a comment isn't the right approach here, would you prefer leaving > the implicit contract as-is, or is an explicit runtime check (such as > VM_WARN_ON_ONCE) something more fitting? We want to silence smatch. Either fix smatch or find a reasonable way to stop it from reporting things that are simply not true. -- Cheers, David