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 36EFE606A323 for ; Tue, 27 Oct 2026 08:06:53 +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=BoIvLyS4 Received: by kanga.kvack.org (Postfix) id 2B1A36B060C; Tue, 27 Oct 2026 04:06:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 284DF6B060D; Tue, 27 Oct 2026 04:06:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 175066B060E; Tue, 27 Oct 2026 04:06:52 -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 DE2C56B060C for ; Tue, 27 Oct 2026 04:06:51 -0400 (EDT) Received: from smtpin18.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 6DDCC1A0908 for ; Tue, 27 Oct 2026 08:06:51 +0000 (UTC) X-FDA: 85367675022.18.5CD0E74 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf28.hostedemail.com (Postfix) with ESMTP id BD646C0006 for ; Tue, 27 Oct 2026 08:06:49 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=BoIvLyS4; spf=pass (imf28.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793088409; b=igqywRI+cMu05ghYlVDD2Y7mJLES0zkB7mMeviks0rBP85ADnr60zGhZex4rUp/cUhK2gg kCR4DFNgqRtT9D5zMujnQ52yOMCfG+4yVCqOqug0yhW37rkETJ/8pOEfqTE4BN139v7Kz4 FYNrNzX1Yk1SiSjftDt1zlvgz/CRrlI= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=BoIvLyS4; spf=pass (imf28.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793088409; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=tGP0LjdymEX/O70OpFiXykL3tGWdkhpJkzQJ0xiHk2s=; b=0dA077fpcIwxwGpO+D4hz2efEIn1sipFIdQMYp0w8DmCRQs9uM2mTLv2PH0Q2eqZuxPpns HxlyToB17L2oxjwFS9h0anHDtSqMNt18o2q4bL0bZaHfRxX/JdQ6DTtjhRckQ7kYzffsbS sr++/42/9OjdaUtfpqkJyeCvUftHQQc= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 44F2243BFB; Tue, 27 Oct 2026 08:06:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7669F1F01825; Tue, 27 Oct 2026 08:06:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793088408; bh=tGP0LjdymEX/O70OpFiXykL3tGWdkhpJkzQJ0xiHk2s=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=BoIvLyS4BeMWr65hedSikSZ5vE8O9JRgtibUW/piTLatgtmus034g8LURA3R+gHJc ydIDPqS/Oq7d7JsbwgaioD3d1cV8JjOomy7xzfXW42dsVa5rjkstyyKLDXODrEKei/ vB2Qwp8dvj5O3AKG6ZMVvpIywISsqf/obj5nk6KOVMT8qLApC1PN0PM0ZrjYBAf2Xu 5g6N2XtIXQ3TbybogpP04e5dcBVdBVy+cHCzH1jEUnk9T+8vtYavS1rB+QxhcGQdgH FThLB2pNS03O7e0SOprSN4uGF5bozDM1GQt3OLElmNxQv6g/clWdchbL3nMOAmhEFL j+r5zdUmZqxow== Date: Tue, 27 Oct 2026 08:06:31 +0000 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (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 Subject: Re: [PATCH 01/46] mm/mglru: don't use stack pointers when walking PUD and PMD tables Message-ID: References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-1-6f74bec9a5bb@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261027-fixes_core-v1-1-6f74bec9a5bb@kernel.org> X-Rspam-User: X-Rspamd-Queue-Id: BD646C0006 X-Stat-Signature: xcttt1f3ipyjfagfquohz95t14h6c3tr X-Rspamd-Server: rspam01 X-Spam-Status: No, score=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=unavailable autolearn_force=no version=4.0.1 X-HE-Tag: 1793088409-560688 X-HE-Meta: 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 53jVRmA5 I2w0SGOWwQJKlMsCsHBU7YnDQAeSkuwoB2VoxkKQ4L8taRgK3TfPjHJcqNGueaU2qeHdLd8zzlIUu5eeKY02maErCzNQKCtEyhhTj7ofMuQ5Osud3IHin3fbyYlK/TCHDWPqkl0L51myTvfkP3e/ASL6tc1G1R/H0/eS3HMr60YnWOMTR4N8W3JyDaJs4dF/qHVRufH7igRo3wlAAiufhupDil4obYXQuOus6i89FFYq3fBhGW4sngV5JH/koconJamkj8Nrh5Q37JvV6QkMbqtG+i8FbbOiJ7eYntfpRD5PJsUVapWpbsiIOO8kwWGM68nC+t1+NiQT5izG3Q7TKETjxRE/2UMgoqCbrZAeNMxiCkIAXiJiXv76qK2n5PC1ETrelqogzKGw1sO3Qc4DZakkWBKo/E6VsC9MY 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 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?... the whole thing feels like NIH syndrome writ large. Anyway, rant aside: Reviewed-by: Lorenzo Stoakes (ARM) > mm/vmscan.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 9959ca158ce83..6a1af9b92349f 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3911,7 +3911,7 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end, > > walk->mm_stats[MM_NONLEAF_FOUND]++; > > - if (!walk_pte_range(&val, addr, next, args)) > + if (!walk_pte_range(pmd + i, addr, next, args)) > continue; > > walk->mm_stats[MM_NONLEAF_ADDED]++; > @@ -3947,7 +3947,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end, > if (!pud_present(val) || WARN_ON_ONCE(pud_leaf(val))) > continue; > > - walk_pmd_range(&val, addr, next, args); > + walk_pmd_range(pud + i, addr, next, args); > > if (need_resched() || walk->batched >= MAX_LRU_BATCH) { > end = (addr | ~PUD_MASK) + 1; > > -- > 2.43.0 > -- Cheers, Lorenzo