From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id E6627606A323 for ; Tue, 27 Oct 2026 19:06:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cje2C2JW Received: by kanga.kvack.org (Postfix) id 8A15A6B08A7; Tue, 27 Oct 2026 15:06:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 879E66B08A9; Tue, 27 Oct 2026 15:06:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 78FC86B08AA; Tue, 27 Oct 2026 15:06:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 416DA6B08A7 for ; Tue, 27 Oct 2026 15:06:34 -0400 (EDT) Received: from smtpin02.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 9AD021A0AC2 for ; Tue, 27 Oct 2026 19:06:33 +0000 (UTC) X-FDA: 85369337466.02.D0FE5F1 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf07.hostedemail.com (Postfix) with ESMTP id E923940007 for ; Tue, 27 Oct 2026 19:06:31 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=cje2C2JW; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf07.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793127991; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=lf2Hoc/RWmB0/QlKnoJRvWNvn+6TzYwCnLWNzrsTcSk=; b=225uTSYATyXeDOWU4VNtfrNe7cI1+XRd3N6Hp2wODerJcUP7RfSDDS/wXXWFJsTNV4NFvc FOyQx+jMQxKHZHDGB4iKWxHeeCocVKnoSckkJ6LsU5eiHYl+DDIIPv1bK4OLEXM/V4GePf zkoRM8FbIMiU3pl4Km6Y0XS6GRrRF58= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=cje2C2JW; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf07.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793127991; b=KhsK3KPSb8lMV0m8pPj85I880Ax+plaX27Rs8Rowan4DAD0SvKEgrOJA9HlU0mhw1goBjx 8oXXIVGYdaSjt64BXrbESz3wAfFpE4XGkATyiges/qSLU6rTsT1h6wGgeX+Y5XqksKcdsg 83HDFU28szuhFXhsbPclRGBHLMLJhBw= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 5D6DD601FE; Tue, 27 Oct 2026 19:06:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CB4261F01825; Tue, 27 Oct 2026 19:06:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793127991; bh=lf2Hoc/RWmB0/QlKnoJRvWNvn+6TzYwCnLWNzrsTcSk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=cje2C2JW/W5/9ZEii8/tlACEPvMOnEjtWQcEG9HwUfuEGalcwYmRITtkhIzXgtM0F zVZPSg6MqWG1EXqB5aEm/UM1ZGW6AUvIBMETQt4ATO4Biy4ylKhaNWcc3aETkNrUX0 +Rs2xhiojhULts3grC2OreKYDtZWNa7jmYsfkJOEIajVofwPjCJtjn26J2BasBa3/1 FBvLrtI8WsnLL8X/8SZDyxn+URbO+XTS1C7Oaenryfso2BZULJrKXufHYlcMtbRIRU EO59ufQ81gNQ6SJ2yjHXTkjfgMYx5Sqa+hoHZTfCdWqAvmQc93hgNF4B+H7JFr5lqG E8VnnHkkgYw3w== Message-ID: Date: Tue, 27 Oct 2026 20:06:09 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 01/46] mm/mglru: don't use stack pointers when walking PUD and PMD tables To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Josef Bacik , stable@vger.kernel.org References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-1-6f74bec9a5bb@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: 7bit X-Rspamd-Queue-Id: E923940007 X-Stat-Signature: wccwug961r6jjkyj9d1kittcpr8i3d9j X-Rspamd-Server: rspam06 X-Spam-Status: No, score=-12.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793127991-31302 X-HE-Meta: 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 DMvi4gOY pihrYF5zbUgsBWzH6hYrkDXcheIDnyOC1sJpgyLM8dersysH+MAXzFH8mLcZLn2zK3Knf9fYYNle0voYLVsGfFQyQ+xw5Cg/w5PFh65j2uLWGnS2FAoOkTRATBNZqYz0OIOWmZxHheoNwUIpobC7FupAdxT8F1FsWX/c5Yu4h6n43OV3PKPLVek06brDkFM868F/DllH3a4/i1K3I6cPI6T9BKhZvavYJyYMq+Hh2nbSxTURxo86FPY/ikltPjnshhAMVCDt/bkVBU9hXgc6wP8zhg8BoHQ4ONYxIVdfWnY2PW7gxLbdOgdjN8bFhsThts7kuqVy0b4mLna6cTFFPT/jYtJ52F0bRRJh7B6jMkvWCnchx628G4GJUMrSNJ5Ke3Q0bNbt1ql8NQLg26umL1DIpVV6oywVw8lDJ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/27/26 09:06, Lorenzo Stoakes (ARM) wrote: > On Tue, Oct 27, 2026 at 12:17:21AM +0100, David Hildenbrand (Arm) wrote: >> From: Josef Bacik >> >> MGLRU passes stack copies of page-table entries in walk_pud_range() and >> walk_pmd_range() when walking to the next level. These copies can become >> stale when khugepaged or MADV_DONTNEED (CONFIG_PT_RECLAIM) removes a PTE >> table concurrently. >> >> This pattern dates back to commit bd74fdaea146 ("mm: multi-gen LRU: >> support page table walks"). Likely, earlier locking masked the latent >> bug. Later changes exposed it: commit 1d65b771bc08 ("mm/khugepaged: >> retract_page_tables() without mmap or vma lock") allowed concurrent >> retraction, and commit cf4a65539c13 ("memcg-v1: no need for memcg locking >> for MGLRU") dropped the walker's outer RCU protection. >> >> The fix is simple, so just fix the original commit so we don't have to >> speculate. To fix it, pass the actual PMD/PUD pointers. This restores the >> RCU-protected lookup and validation against the live PMD. Note that the PUD >> handling is required as well to handle folded page tables correctly in all >> cases. >> >> Fix generated by an LLM and sent by Josef Bacik in private. >> >> Fixes: bd74fdaea146 ("mm: multi-gen LRU: support page table walks") >> Cc: stable@vger.kernel.org >> Signed-off-by: Josef Bacik >> [ david: handle walk_pud_range() as well, clarify+simplify description, >> adjust Fixes: ] >> Signed-off-by: David Hildenbrand (Arm) >> --- > > God, terrible. And why does MGLRU feel it needs its own independent page > walking mechanism?... It's all a big mess. I think at LSF/MM there was some talk of using that also for traditional LRU, but I guess it might take a while ... -- Cheers, David