From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1D11338AC88 for ; Fri, 28 Aug 2026 23:17:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787959073; cv=none; b=nMxOvaWr1jgbayJhBViA6AYY61OnEJovYYpOM9qGxFyxs/r6d0yjdWp26udVz5tW5aoMfAYk+/mxFnhxnF3XxS+YDJUtu5UalT2US0d26qpPb7IJQ5FQlnZyQXXlgOIkjd4JRv9/h6/mO3CM2m6yePpcvnaXBzkTBI6zn8+WtF0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787959073; c=relaxed/simple; bh=XJ0DDbvRh0gWy8lOQVtFXpsocWWYUAELD35TdZeq85I=; h=Date:To:From:Subject:Message-Id; b=EwttqjugHP/k9T8YgxEbD0puxXxig+tkvuaK3/2a2xZ2j0FRkAnrxhWUhuPSDo5m2Qvu+yHWeDrnWKoOcKlUVlQxafJPew0hnnUNv1F4kxytGGxWd/SsF9O8hjkfQb9HMcwNXyHPmBrCIWnHYmhmIRTaDhxxVwyvoUUQSryh8ak= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=e/8a5bmm; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="e/8a5bmm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB2391F000E9; Fri, 28 Aug 2026 23:17:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1787959072; bh=ggLQHTbUH0Ai7e85mPwPqTIh4w1BMjSDhuR+4d7XdlA=; h=Date:To:From:Subject; b=e/8a5bmmbT7MZ0IVQ7FBJpDOdkRaEni+LGa30e1RotZIpAEnNp6B2ZLv0rps41xO8 yGCCyzcBoYVF+MYA1k2egGKLPogZBvEzyqNZNTCbDpWKabj5LctHtrfUFq7hgtW1ja e9JIkfNcCpTJ3B9hgiTQ8wgmEqBU1LxnCogq0lPs= Date: Fri, 28 Aug 2026 16:17:51 -0700 To: mm-commits@vger.kernel.org,ziy@nvidia.com,yuzhao@google.com,yuanchu@google.com,weixugc@google.com,vbabka@kernel.org,shakeel.butt@linux.dev,roman.gushchin@linux.dev,ridong.chen@linux.dev,qi.zheng@linux.dev,muchun.song@linux.dev,mhocko@kernel.org,ljs@kernel.org,lianux.mm@gmail.com,liam@infradead.org,hannes@cmpxchg.org,david@kernel.org,chrisl@kernel.org,baoquan.he@linux.dev,baolin.wang@linux.alibaba.com,baohua@kernel.org,axelrasmussen@google.com,kasong@tencent.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-mglru-fix-potential-generation-folio-number-leak.patch added to mm-new branch Message-Id: <20260828231751.EB2391F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/mglru: fix potential generation folio number leak has been added to the -mm mm-new branch. Its filename is mm-mglru-fix-potential-generation-folio-number-leak.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-fix-potential-generation-folio-number-leak.patch This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next If a few days of testing in mm-new is successful, the patch will me moved into mm.git's mm-unstable branch, which is included in linux-next Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Kairui Song Subject: mm/mglru: fix potential generation folio number leak Date: Wed, 26 Aug 2026 01:53:39 +0800 Each generation of MGLRU accounts anon and file folio numbers separately, and the page table walker updates each generation's counters in batch once the walk is done. The walker promotes a folio's generation with a cmpxchg on folio->flags, and update_batch_size() then reads the live flags again to pick the anon/file column to charge. The walk holds neither the lruvec lock nor the folio lock, so the type can flip between the cmpxchg and that read: the lazyfree path clears PG_swapbacked, and reclaim sets it back on a dirty lazyfree folio. The batched delta pair is then recorded in the wrong type column. Nothing reconciles it afterwards, permanently skewing lrugen->nr_pages and the reclaim budgets derived from it. Fix it by capturing the type from the flags snapshot the cmpxchg linearized against: folio_update_gen() returns the type of the state it transitioned from, and update_batch_size() accounts with that. A folio's type only changes while it is off the LRU list, inside a del/add pair under the lruvec lock, with the gen bits cleared in between. The generation and PG_swapbacked sit in the same folio->flags word, so the cmpxchg snapshot captures them together. Let G be the generation that snapshot captured (old_gen) and G' the one it wrote (new_gen); the CAS can land in only three places: - before the del: the folio is anon at G; the batch records anon G -> G', and the del later removes the folio from the anon counters; - between del and add: gen == -1, so folio_update_gen() returns -1 without touching the flags and no batch is recorded; the del/add pair accounts for the move alone; - after the add: the folio is file at the fresh generation the add charged; the batch records file, that gen -> G', matching that charge. Unlike the drift of lazy promotions, which sort_folio() repairs under the lruvec lock, the phantom deltas from before this fix land in a column the folio never occupies again, so nothing ever repairs them. Link: https://lore.kernel.org/20260826-mglru-flags-cleanup-v3-6-d9f1c75549c8@tencent.com Fixes: 018ee47f1489 ("mm: multi-gen LRU: exploit locality in rmap") Signed-off-by: Kairui Song Cc: Axel Rasmussen Cc: Baolin Wang Cc: Baoquan He Cc: Barry Song Cc: Chris Li Cc: David Hildenbrand (Arm) Cc: Johannes Weiner Cc: Liam R. Howlett Cc: Lian Wang Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Muchun Song Cc: Qi Zheng Cc: Ridong Chen Cc: Roman Gushchin Cc: Shakeel Butt Cc: Vlastimil Babka Cc: Wei Xu Cc: Yuanchu Xie Cc: Yu Zhao Cc: Zi Yan Signed-off-by: Andrew Morton --- include/linux/mm_inline.h | 7 ++++++- mm/vmscan.c | 13 +++++++------ 2 files changed, 13 insertions(+), 7 deletions(-) --- a/include/linux/mm_inline.h~mm-mglru-fix-potential-generation-folio-number-leak +++ a/include/linux/mm_inline.h @@ -10,6 +10,11 @@ #include #include +static inline int folio_flags_is_file_lru(const unsigned long *flags) +{ + return !test_bit(PG_swapbacked, flags); +} + /** * folio_is_file_lru - Should the folio be on a file LRU or anon LRU? * @folio: The folio to test. @@ -27,7 +32,7 @@ */ static inline int folio_is_file_lru(const struct folio *folio) { - return !folio_test_swapbacked(folio); + return folio_flags_is_file_lru(const_folio_flags(folio, 0)); } static __always_inline void __update_lru_size(struct lruvec *lruvec, --- a/mm/vmscan.c~mm-mglru-fix-potential-generation-folio-number-leak +++ a/mm/vmscan.c @@ -3269,7 +3269,8 @@ static bool positive_ctrl_err(struct ctr ******************************************************************************/ /* promote pages accessed through page tables */ -static int folio_update_gen(struct folio *folio, int new_gen, const vma_flags_t *vma_flags) +static int folio_update_gen(struct folio *folio, int new_gen, int *is_file, + const vma_flags_t *vma_flags) { unsigned long new_flags, old_flags = READ_ONCE(*folio_flags(folio, 0)); int old_gen; @@ -3298,6 +3299,7 @@ static int folio_update_gen(struct folio new_flags |= BIT(PG_workingset); } while (!try_cmpxchg(folio_flags(folio, 0), &old_flags, new_flags)); + *is_file = folio_flags_is_file_lru(&old_flags); return old_gen; } @@ -3328,9 +3330,8 @@ static int folio_inc_gen(struct lruvec * } static void update_batch_size(struct lru_gen_mm_walk *walk, struct folio *folio, - int old_gen, int new_gen) + int old_gen, int new_gen, int type) { - int type = folio_is_file_lru(folio); int zone = folio_zonenum(folio); int delta = folio_nr_pages(folio); @@ -3519,7 +3520,7 @@ static bool suitable_to_scan(int total, static void walk_update_folio(struct lru_gen_mm_walk *walk, struct vm_area_struct *vma, struct lruvec *lruvec, struct folio *folio, bool dirty) { - int new_gen, old_gen; + int new_gen, old_gen, file; if (!folio) return; @@ -3532,9 +3533,9 @@ static void walk_update_folio(struct lru folio_mark_dirty(folio); if (walk) { - old_gen = folio_update_gen(folio, new_gen, &vma->flags); + old_gen = folio_update_gen(folio, new_gen, &file, &vma->flags); if (old_gen >= 0 && old_gen != new_gen) - update_batch_size(walk, folio, old_gen, new_gen); + update_batch_size(walk, folio, old_gen, new_gen, file); } else if (lru_gen_set_refs(folio, &vma->flags)) { old_gen = folio_lru_gen(folio); if (old_gen >= 0 && old_gen != new_gen) _ Patches currently in -mm which might be from kasong@tencent.com are mm-memcontrol-make-lru_zone_size-atomic-and-simplify-sanity-check.patch mm-mglru-introduce-helpers-for-manipulating-gen-and-refs-flags.patch mm-migrate-copy-all-referenced-state-via-folio_migrate_lru_refs.patch mm-mglru-move-max_seq-read-into-walk_update_folio.patch mm-mglru-use-explicit-tier-range-in-read_ctrl_pos.patch mm-mglru-fix-potential-generation-folio-number-leak.patch