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 6D4FA4A43E5 for ; Tue, 1 Sep 2026 22:40:45 +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=1788302448; cv=none; b=Rmuq3z+YeDeJwwvR6yL5YEIqHw7vEquk1ts6+gbKUwoik8R6LyEA6vaxN98B22fcldljihquXDCa+49VRUl90tYYxiapvJAImAMcGtT3vs3HVFqIbInZZlRFkEZ6x6b43/d6OJGmOSAo59k4DGconeqqZQRcL3K+1mokfTYoZ18= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788302448; c=relaxed/simple; bh=pYB09fa9G8Pn2gPL2vPWrLZzMj+FKVkOsEe/Xw4mm9o=; h=Date:To:From:Subject:Message-Id; b=fWmi6e+fkCUTpFniR2uJYYLCweoyTPGgtcPX/2OtQclakOU1qWinuL5FabaGDfQEBR6EoPoHzpodmzKOSqlmBJtO0vnXTNV7t2SWtCMf0zPA5MgGivrasFzKL1clwLcPWZuVXgcgarg9dEs6fvCR1zBeNpExRMH6jAF3gwjtvSc= 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=WZJWyUT2; 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="WZJWyUT2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DEFF71F00A3A; Tue, 1 Sep 2026 22:40:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1788302443; bh=OQwLRPjuCqg3c17C5P1yieQeURbCEHVHDD2Y1JlBl74=; h=Date:To:From:Subject; b=WZJWyUT2VsSDjb4cqaO2T38b6RXai4Iznpmy6EFzvcAmTpucQOg9toUN4j7P0SeIy E/cgEDlbk7oczB8peEAkXX62dBbXJVXv3ohYCdz5fE7alBRzzdukI7tras/ag6Ml+7 RGa38Hzzv6ZKAwOhfLdefQCPP1W0RCUwg3kL+/aA= Date: Tue, 01 Sep 2026 15:40:42 -0700 To: mm-commits@vger.kernel.org,kasong@tencent.com,akpm@linux-foundation.org From: Andrew Morton Subject: [to-be-updated] mm-mglru-fix-potential-generation-folio-number-leak.patch removed from -mm tree Message-Id: <20260901224042.DEFF71F00A3A@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/mglru: fix potential generation folio number leak has been removed from the -mm tree. Its filename was mm-mglru-fix-potential-generation-folio-number-leak.patch This patch was dropped because an updated version will be issued ------------------------------------------------------ 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