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To: Gregory Price Cc: Zi Yan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, vbabka@suse.cz, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org References: <20251020170615.1000819-1-gourry@gourry.net> <487730c6-423a-4a03-a668-9b9ff92a5cfb@redhat.com> <609E7E01-33A6-4931-AC89-1F4B2944FB64@nvidia.com> <272c425a-b191-4eef-af6e-2bca1db7a940@redhat.com> <0d92a675-ab24-4b1c-be71-956f09a9e973@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: 47JPoXbVnorDqCtXwO_aSVjbqLEQ6cVOpC_caQCwoiE_1760991465 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: rspam10 X-Rspamd-Queue-Id: 721F91A0010 X-Stat-Signature: uqjt5d4yfrxnt5bynhu1jbinbhhsjbyq X-Rspam-User: X-HE-Tag: 1760991470-780997 X-HE-Meta: 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 iA8HwhG4 QbiXe/Bv2SuAyvbNkSC0RS9+ZcgkTy+EvXX2fkj+s7Dk+FgjIzRVERZiMz+RLvIZFdOA/64M8Pyh3sBRORKyIYkOsnabDlIDner99WZiNJaDThuFsLdR2PCn4W6JonzH3Z2v5ISniDMEbMoq+nTwgAVFZCjuR6kPmBVi+Aqz6p2Gere6Trhti8FYQfJz+JqbdW7UpLIWyb6KXaxD7sDH+nfowFq+umeLXaqELa7ppdwxBfjmu2YO+G7Wu6XZChF2hLVIUfJhio3BN1jJHm2Zqvzc19OOLfCPihFU6303W51VeAzVgZItL5PRW6x9r49qzcC2VLFl/zUcCMP1DsWPRjUk0eOQLYQGRKynhBDDpDMnspvM2iWM2JFyY15/cme45SkWu2ZDES07O08yb/EvgUmwAliyjRdZaR+G9geUTySweXbC3AWhycUtIoPUR6jzmvj058XMoUJzu2ZEj3B0+oVLkFTF84lB8FF3B 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 20.10.25 21:58, Gregory Price wrote: > On Mon, Oct 20, 2025 at 09:46:21PM +0200, David Hildenbrand wrote: >> On 20.10.25 21:40, Gregory Price wrote: >>> On Mon, Oct 20, 2025 at 09:18:36PM +0200, David Hildenbrand wrote: >>>>> >>>>> Basically, what is the right way of checking a folio order without lock? >>>>> Should we have a standardized helper function for that? >>>> >>>> As raised, snapshot_page() tries to stabilize the folio best it can. >>> >>> is snapshot_page() even worth it if we're already racing on flag checks? >> >> I think it tries to handle what compound_order() cannot easily handle, as it >> will retry in case it detects an obvious race. >> >>> >>> i.e. there's already a race condition between >>> >>> pfn_range_valid_contig(range) -> compaction(range) >> >> Can you elaborate how compaction comes into play here? I'm missing the >> interaction. >> >> pfn_range_valid_contig() should be only called by alloc_contig_pages() and >> not out of compaction context? >> > > I've been digging through the code a bit, so a quick shot from my notes > > alloc_contig_pages_noprof > if (pfn_range_valid_contig(range)) <- check validity > __alloc_contig_pages(range) > alloc_contig_range_noprof(range) > start_isolate_page_range(range) <- isolate > __alloc_contig_migrate_range(range) > isolate_migratepages_range(range) <- compact Oh, that's what you mean with "compact", it's just isolation+migration. > > Seems like all the checks done in pfn_range_valid_contig() already race > with everything after it anyway since references aren't held? Any of > those pages could be freed (get bogus values), but i suppose not > allocated (given the zone lock is held)? Yes, it's completely racy. I was primarily concerned about us calling functions that will VM_WARN_ON() etc due to the races; not that they would make us accept/jump over a range although we shouldn't. Of course, regarding the latter, we want to try as good as possible to avoid jumping over ranges that we can actually handle. -- Cheers David / dhildenb