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[2003:d8:2f3f:f800:c101:5c9f:3bc9:3d08]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e2a996bf1sm73938005e9.1.2025.09.25.04.06.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Sep 2025 04:06:59 -0700 (PDT) Message-ID: <7305f905-0f81-4268-a3b3-933ac00cdb6a@redhat.com> Date: Thu, 25 Sep 2025 13:06:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: always call rmap_walk() on locked folios To: Lokesh Gidra , Dan Williams , Alistair Popple Cc: akpm@linux-foundation.org, linux-mm@kvack.org, kaleshsingh@google.com, ngeoffray@google.com, jannh@google.com, Lorenzo Stoakes , Harry Yoo , Peter Xu , Suren Baghdasaryan , Barry Song , SeongJae Park References: <20250918055135.2881413-1-lokeshgidra@google.com> <20250918055135.2881413-2-lokeshgidra@google.com> <2c9df5ee-6109-4fa5-b895-ad8e47d34bee@redhat.com> <5549ac3a-20cf-4959-ac53-0a89ed0eadd2@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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: eLyvZXd9VK4TsE-TpOy8tVearDbGOSpteAAH9_cit2A_1758798421 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 342E940017 X-Stat-Signature: xog7bdd5jd7phgeg8eurp9ri4boi6act X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1758798424-525438 X-HE-Meta: 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 sSmSSX+/ jEp5pnN74BLC2qeGR6xY4JyRRdUqPCfwOPyPmVLXfGiI53wjoSHkfr6sM/BKf17+iXNZkziJ9AL8TcnSzda2FoPRDlAjgHFE9Yl3Ccd2Wq8FRmZPtOxMXUWUwRQpiukuZk6LE/BOfo2SwYjCbkmz7ObXK98CQtbTal9VClJUU6eMbSEqRcgkAoHfWhaqKe+STht2Nep29NUy/b5mpB1+z7X6DJCTGlNsF7rO6DlE5yP8mLa4YFbdfSD24iK4EFImHzDZ99kdCxy68Tg65KZFS/69Fl4N/wdNJjYu/0JW0Imdop4TliEqLFB1yBIPZvhIqSea5wLo83TrlVw+SGxidIGYP+LpTEM+S6txFXuDLSd4UpT09flLxT7im8nsfn3gM45p7feDzj53GELkECb4fM+cfidqvc49UYzUcGzK9B4LPvCrFxOpgxSPKMxSQTCIrLWYRhGITWDg5yCnzm52HykupPr8l7McRm+YHlgaqWEOsAmk= 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: On 24.09.25 21:17, Lokesh Gidra wrote: > On Wed, Sep 24, 2025 at 3:00 AM David Hildenbrand wrote: >> >>>> >>>> Is mf_generic_kill_procs()->collect_procs() problematic? >>>> >>>> The dax_lock_folio/dax_unlock_folio part confuses me: I think it only >>>> locks an entry in the page cache but not the actual folio ("Lock the DAX >>>> entry corresponding to a folio")? >>> Yeah. The name dax_lock_folio() gives an impression as if the folio is >>> locked but it isn't :) >> >> Sorry for the late reply, I saw you posted v2 in the meantime. >> >>> >>> IIUC, a dax folio can't have an anon_vma (folio->mapping is actually >>> an address_space instead of anon_vma), right? >> >> We have these weird device-private dax folios that are anonymous and >> should have the anon_vma set up. >> >>> So, I thought it wasn't >>> required to actually lock the folio in this case. Please let me know >>> if you want me to still lock the folio around collect_procs(), or add >>> a comment? >> >> I think we can end up reaching memory_failure_dev_pagemap() with an >> anonymous dax folio. >> >> Not sure if anything would prevent us into calling >> >> mf_generic_kill_procs()->collect_procs()->collect_procs_anon()->folio_lock_anon_vma_read() >> > I must be missing something but dax_lock_folio() dereferences Maybe the code is missing something :) > folio->mapping (to get to host) without checking for > FOLIO_MAPPING_FLAGS presence. If it were an anon folio, wouldn't that > be a problem? And then in collect_procs() we obviously check for > folio_test_anon() on the same folio before calling > collect_procs_anon(). Right, if we reach dax_lock_folio() with an anon folio we are probably already messing things up? Not sure if the "!dax_mapping(mapping)" would save us, likely not, because it would be an anon_vma. Hopefully Dan+Alistair have a clue how this works and if it already works as expected with device-private anon folios. -- Cheers David / dhildenb