From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 42C00606A320 for ; Tue, 27 Oct 2026 19:06:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=VlxXa6M5; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cje2C2JW DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Unsubscribe-Post: List-Owner; bh=lf2Hoc/RWmB0/QlKnoJRvWNvn+6TzYwCnLWNzrsTcSk=; b=VlxXa6M5GNcP5d xeHepQdTdxL+4LBNdkwd1KCkF7IMPhqwwZpMXbE6IuhLRnXs28w+HNXFH01oh30AwSRe3MSdBW0G7 Rr7CKbYpQ+MakhhT+eoH3tmXvIqD2nJLw4Jl6yF37szOkxDEnB/vasTQZ040S6b4+9krPeRj/5Kbx bef7EjufoPYWCPpVaxoLaq0fRpXRDpTl2nQsbZ+K3/PgQ/VGV/E7gEIah74+TVs57A2z/lk/jo1Dv K8UaG16uIomfXBbg7nieruWpmNHjUFN/47yKuJ5gy1djj2+J217AiqJ9ERBAb1gNnil+PRNdD2HGC H11jGyfHxu/XbXUXBxAw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xLmVG-00000005ciM-1w6R; Tue, 27 Oct 2026 19:06:34 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xLmVE-00000005ci7-3Q5N for kexec@lists.infradead.org; Tue, 27 Oct 2026 19:06:32 +0000 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; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" X-Spam-Status: No, score=-12.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 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