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[2003:d8:2f20:da00:b70a:d502:3b51:1f2d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e7d9844d24sm1148099f8f.46.2025.09.12.09.04.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Sep 2025 09:04:16 -0700 (PDT) Message-ID: <5617a501-3f46-423e-b3da-98efcd63d7c7@redhat.com> Date: Fri, 12 Sep 2025 18:04:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 05/15] mm, swap: always lock and check the swap cache folio before use To: Kairui Song , linux-mm@kvack.org Cc: Andrew Morton , Matthew Wilcox , Hugh Dickins , Chris Li , Barry Song , Baoquan He , Nhat Pham , Kemeng Shi , Baolin Wang , Ying Huang , Johannes Weiner , Yosry Ahmed , Lorenzo Stoakes , Zi Yan , linux-kernel@vger.kernel.org, Kairui Song References: <20250910160833.3464-1-ryncsn@gmail.com> <20250910160833.3464-6-ryncsn@gmail.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: <20250910160833.3464-6-ryncsn@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Phq4CCNS3IT6svJ9xpMomGN8FgHvC3NulC0upd3RNN4_1757693058 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: rspam11 X-Rspamd-Queue-Id: 79AB740014 X-Stat-Signature: 46s1zkjh1bfyru5wk7zaei7psu4scua4 X-Rspam-User: X-HE-Tag: 1757693061-368206 X-HE-Meta: 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 51LPPF8U Hvscn1s1eY4WXcJ06syIKsouGBvf3JiWBJ2BiGSauZQqTOLD7a1wY7/jAqPHE1Rpy1oB6pFLqMu2hCZI3W1vjRFjwMDDf0U69t9nOCe0CtKCfwYKMj9MsyUU5udkZUzhRDgOdzTAC2v1gfvlNFZz6DQ3H0PxgOvi7jkVxmTzPc4Kr1W1mWCPY3LOvvv1L50J1ZakfVmt+WIeGI//FHHRf/a7bi+OtLax2L0Pc0A64M9zYXcvR/9abpW44xCt+SeGt4TkP98Qa5MVhBVsSmTqltKgt9czY3X4AkAJv0k2NC7FKrtJ/u5up3PH1bd8CbCfIZ9HYjZkWGFwqq+XwYd/EGto2cMwtrKrALogBhT56qSGLJy21ysgk74P+6/doSaqqc/7wG4vbVcwj1DFEyo2C0/pihhriCqrLdeCX9D6sB3ra0Wj23BvNTwgfoIcS8KeeRJId 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 10.09.25 18:08, Kairui Song wrote: > From: Kairui Song > > Swap cache lookup only increases the reference count of the returned > folio. That's not enough to ensure a folio is stable in the swap > cache, so the folio could be removed from the swap cache at any > time. The caller should always lock and check the folio before using it. > > We have just documented this in kerneldoc, now introduce a helper for swap > cache folio verification with proper sanity checks. > > Also, sanitize a few current users to use this convention and the new > helper for easier debugging. They were not having observable problems > yet, only trivial issues like wasted CPU cycles on swapoff or > reclaiming. They would fail in some other way, but it is still better to > always follow this convention to make things robust and make later > commits easier to do. > > Signed-off-by: Kairui Song > --- [...] > index 4baebd8b48f4..f1a4d381d719 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -240,14 +240,12 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si, > * Offset could point to the middle of a large folio, or folio > * may no longer point to the expected offset before it's locked. > */ > - if (offset < swp_offset(folio->swap) || > - offset >= swp_offset(folio->swap) + nr_pages) { > + if (!folio_matches_swap_entry(folio, entry)) { > folio_unlock(folio); > folio_put(folio); > goto again; > } > offset = swp_offset(folio->swap); > - Nit: unrelated change. Acked-by: David Hildenbrand -- Cheers David / dhildenb