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[2003:d8:2f1f:3f00:731a:f5e5:774e:d40c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b66bbcf19sm164087935e9.4.2025.09.02.03.18.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 Sep 2025 03:18:28 -0700 (PDT) Message-ID: <911dc3b4-c511-4ef2-a159-091780987965@redhat.com> Date: Tue, 2 Sep 2025 12:18:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/9] 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 References: <20250822192023.13477-1-ryncsn@gmail.com> <20250822192023.13477-3-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: <20250822192023.13477-3-ryncsn@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: C2FHLsFs7p4brvOqFx4ZVN9N332PuIRtkQweEmKlonk_1756808311 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: DB1F6160016 X-Stat-Signature: zrdg9wczkuqkwi5a5hd4jzn936dga1k4 X-HE-Tag: 1756808315-266699 X-HE-Meta: U2FsdGVkX19XULCTMmKNMLsL/ZI121lbPGABnDkjCtmYGymQYj7brlI+cCDXJSG90FVa7bfNDk5E1OfWYRw6RAoeTqVTL9qf2z9Pyfekw4+dy6snITpw57/5D5VA+30bNOjopevQDkWq2DQTofxpeg4lJBz/rjDbuqQX119w96aJBPR6iIBoAEfaw0opE/KYxGxo/9/9wbQwvinbHlLUULRa5A71wg/qPbPX/nswQq5rilUCzsBA6nzHiKstBQxgki7jN0SiZuc9aFR/9gb6zqh64pTzofhJQCBnZg8lNAXezDB3wfHOS+wtsllG4HY2zaUiD2kxaqejLPGA3pR9j2gciu/Pfy/aKNVYGIEJr89YnPhO084E6UU7rmf8PcbK4uKe6Z37K1hlGb5de/0LAhh24J6H9x9s6NG8Iyt8kFvFe1GRX+gzT3oZeyHl5eCep2tv6xpyns+ZfEdwHANcfyH8W4el1vX1nFAmUsrujmaUrbq5orsfv//ZvjUwSGtLL2qNCrxaywDEpwdxnjWvUKevQe8VBo7dvIpcnfU4piv+RBAe8p0abt9sCic6rUlWeJw41wdwwiKU/WfdpQFtlONw+QpbD3zTI2rbO8cK38gwCG7HA2bTZ19dTTasgzj4BFltxjcJ6JuThyuYq1YAuA4MAdui6iyBxkRtj4UPqT1CIkS59osoAcZejMWetxAXdLmTC8IOPRJr7F2DuAYHoWamiQt6ckQwYQi+WHK+nzPdGmjs2wMD4GGJ9xQ3zzV0Gvy4vIRYadxuX1PWQ8zGsW8x52LT4fezYyKndOklm9W+/uE1nUgjYZ4xsV22xrH12gvHB+0zJTbfRX+ibfoSyYZulWydgo3TYWxxB56Fjo3f8+egbO886IdlhCGi7kD5MUnKf47y0x2SbVKkBRgdxgn0J+rtlEizo32bf15yt8/T39+jiHrhWeg3FEJKE1am2Ha+yezLIHACMyAnVvf a88xkKcy 4xb1VCnk5z/4aRMeboB16Y5YUykpky+MMpi0yDL7179x8qZejxcOFBWXNgo6F0L17QPHlccuc07fBzlVJozQcjxf0rNXtGVd4kfOCxcDBBMpKh3woJl/Azp6JRuGm5Z+RfowpxjBgaeKrnq/yqNeFS4JdyeeKy53q1dcCNyEhLbjzYBeRUE9WnzX1k/kIBrzt3V0nIdtXtIsrzsxrPREa9R+0Nbl0BZbYpMS/DYzj4ilKRdvttlYw+pG+El3gslIg+EOICL+5PLpy893iYD4QEHq+ut5aIUvyNAIIezDL4N7XMiZm4bIUmVlDABQu4OJSy1ZBdtW7lm6QvjdlJGbCbWi4UueVwSoEpYsO9eZi2q6DJPEGAfoXpoC7HTHYiL1VimMt35gl7iPD4MzTVXWv8ZDlaa5D4/SstnBKRfdYwDjCoV9Th6TJv5k+KdREd/7qopwJL+f/qfoJkCQ= 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 22.08.25 21:20, Kairui Song wrote: > From: Kairui Song > > Swap cache lookup is lockless, it 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 always has to lock and check the folio before use. > > Document this as a comment, and introduce a helper for swap cache folio > verification with proper sanity checks. > > Also, sanitize all current users to use this convention, and use the new > helper when possible for easier debugging. Some existing callers won't > cause any major problem right now, only trivial issues like incorrect > readahead statistic (swapin) or wasted loop (swapoff). It's better to > always follow this convention to make things robust. > > Signed-off-by: Kairui Song > --- [...] > +/** > + * folio_contains_swap - Does this folio contain this swap entry? > + * @folio: The folio. > + * @entry: The swap entry to check against. > + * > + * Swap version of folio_contains() > + * > + * Context: The caller should have the folio locked to ensure > + * nothing will move it out of the swap cache. > + * Return: true or false. > + */ I appreciate the kerneldoc. Intuitively, this should be called "..._swap_entry". But I wonder if "contains" is really the right term to use here. It's more like that a swap entry "belongs to" (was assigned to) a folio, right? Sure, we store the information in the folio, but the "contains" is a bit weird. folio_matches_swp_entry() maybe? > +static inline bool folio_contains_swap(struct folio *folio, swp_entry_t entry) > +{ const struct folio * > + pgoff_t offset = swp_offset(entry); > + > + VM_WARN_ON_ONCE(!folio_test_locked(folio)); > + if (unlikely(!folio_test_swapcache(folio))) > + return false; > + if (unlikely(swp_type(entry) != swp_type(folio->swap))) > + return false; > + return offset - swp_offset(folio->swap) < folio_nr_pages(folio); > +} > + > void show_swap_cache_info(void); > void *get_shadow_from_swap_cache(swp_entry_t entry); > int add_to_swap_cache(struct folio *folio, swp_entry_t entry, > @@ -144,6 +167,11 @@ static inline pgoff_t swap_cache_index(swp_entry_t entry) > return 0; > } > -- Cheers David / dhildenb