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 22A063A7F48 for ; Tue, 14 Jul 2026 03:21:02 +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=1783999264; cv=none; b=oRnyiwkcJxw8iUl26ahA6VxLmFUAuiQweOz3EO+iVxSsFy2BYnepXtv7B/o7qlM9WK3hZtXaWRdLwoBjXkVW6MzEIhjJgfLiiMdZIZjqf01jiDOJfNxfzl3hW9bHQtFKoZqSeqFu+I5IPPln4qnvkvYUP5RvDp8ZF20hV191B8E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783999264; c=relaxed/simple; bh=qpvExZqCyQ2DYRnf5U7TPeWAUPgouqoQSsDkTRUPgAs=; h=Date:To:From:Subject:Message-Id; b=FR5+TroHhct94ypkf3uI7YkrPsGWyAbDOM54gvpS75e2g2PSDxe5QOAEFwuFsbldzvNL5xERum7SReMFP6wpxoCAB/6pVK96FZ6QmEXDFuCsAWucp3/D5Ih9WHvrhq8DMIAfZ6KrfdN3Ydfza+J37rLSwH8Q/aJ57NYoMtWkQqE= 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=neLFO9+7; 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="neLFO9+7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 99CF91F000E9; Tue, 14 Jul 2026 03:21:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1783999262; bh=iJww7fmMiI9eSXEkuzxroBsM/mX6uligA21JsgC3P4g=; h=Date:To:From:Subject; b=neLFO9+7BK3SSnBFBzVpfF3/fu+zFB7WHxwvuAX6DICmldZBdsISiuQj5AA7K5kNj 7ENLgNHz1/3ckv8suta2YUQkMOpNPxbsaQyKxxvuJ5MSE5w/SFHhdzfrnZ3iQYz3zz mnJx2KeqnDynPRVd7FgEr56ml80StF7bP2qlxA+g= Date: Mon, 13 Jul 2026 20:21:02 -0700 To: mm-commits@vger.kernel.org,ye.liu@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-page_owner-use-memcg_data-snapshot-to-avoid-toctou-in-print_page_owner_memcg.patch added to mm-unstable branch Message-Id: <20260714032102.99CF91F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/page_owner: use memcg_data snapshot to avoid TOCTOU in print_page_owner_memcg() has been added to the -mm mm-unstable branch. Its filename is mm-page_owner-use-memcg_data-snapshot-to-avoid-toctou-in-print_page_owner_memcg.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_owner-use-memcg_data-snapshot-to-avoid-toctou-in-print_page_owner_memcg.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm 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: Ye Liu Subject: mm/page_owner: use memcg_data snapshot to avoid TOCTOU in print_page_owner_memcg() Date: Tue, 14 Jul 2026 09:51:08 +0800 print_page_owner_memcg() takes a snapshot of page->memcg_data via READ_ONCE at the top of the function and guards against tail pages and NULL memcg_data. However, it later calls two functions that re-read page->memcg_data locklessly: 1) page_memcg_check(page) — re-reads page->memcg_data; 2) PageMemcgKmem(page) — calls folio_memcg_kmem(), which re-reads folio->memcg_data and folio->page->compound_head, wrapping both in VM_BUG_ON assertions: VM_BUG_ON_PGFLAGS(PageTail(&folio->page), &folio->page); VM_BUG_ON_FOLIO(folio->memcg_data & MEMCG_DATA_OBJEXTS, folio); If the page is concurrently freed and reallocated as a THP tail page or a slab page between the initial guards and these later calls, the VM_BUG_ON assertions can fire on debug builds (CONFIG_DEBUG_VM=y), causing a kernel panic. Fix both TOCTOU issues by using the memcg_data snapshot throughout: - Extract objcg from the snapshot via objcg = (void *)(memcg_data & ~OBJEXTS_FLAGS_MASK) instead of calling page_memcg_check(page); - Test (memcg_data & MEMCG_DATA_KMEM) instead of calling PageMemcgKmem(page), which is semantically equivalent: PageMemcgKmem()->folio_memcg_kmem()->folio->memcg_data & MEMCG_DATA_KMEM. - When memcg_data has MEMCG_DATA_OBJEXTS set, early-return after printing "Slab cache page\n" since objcg != memcg for slab pages and there is no meaningful cgroup to look up. This avoids both TOCTOU windows and the assertions entirely. Link: https://lore.kernel.org/20260714015117.78351-10-ye.liu@linux.dev Signed-off-by: Ye Liu Reviewed-by: Zi Yan Cc: Brendan Jackman Cc: Johannes Weiner Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Suren Baghdasaryan Cc: Vlastimil Babka (SUSE) Signed-off-by: Andrew Morton --- mm/page_owner.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) --- a/mm/page_owner.c~mm-page_owner-use-memcg_data-snapshot-to-avoid-toctou-in-print_page_owner_memcg +++ a/mm/page_owner.c @@ -540,6 +540,7 @@ static inline int print_page_owner_memcg struct page *page) { unsigned long memcg_data; + struct obj_cgroup *objcg; struct mem_cgroup *memcg; bool online; char name[80]; @@ -549,11 +550,14 @@ static inline int print_page_owner_memcg if (!memcg_data || PageTail(page)) goto out_unlock; - if (memcg_data & MEMCG_DATA_OBJEXTS) + if (memcg_data & MEMCG_DATA_OBJEXTS) { ret += scnprintf(kbuf + ret, count - ret, "Slab cache page\n"); + goto out_unlock; + } - memcg = page_memcg_check(page); + objcg = (void *)(memcg_data & ~OBJEXTS_FLAGS_MASK); + memcg = objcg ? obj_cgroup_memcg(objcg) : NULL; if (!memcg) goto out_unlock; @@ -561,7 +565,7 @@ static inline int print_page_owner_memcg cgroup_name(memcg->css.cgroup, name, sizeof(name)); ret += scnprintf(kbuf + ret, count - ret, "Charged %sto %smemcg %s\n", - PageMemcgKmem(page) ? "(via objcg) " : "", + (memcg_data & MEMCG_DATA_KMEM) ? "(via objcg) " : "", online ? "" : "offline ", name); out_unlock: _ Patches currently in -mm which might be from ye.liu@linux.dev are mm-page_owner-extract-skip_buddy_pages-helper-to-unify-buddy-page-skipping.patch mm-page_owner-add-mr_never-to-enum-migrate_reason-and-use-it-for-last_migrate_reason.patch mm-use-enum-migrate_reason-instead-of-int-for-migration-reason-parameters.patch mm-page_owner-hoist-config_memcg-to-function-level-for-print_page_owner_memcg.patch mm-page_owner-add-missing-newline-to-count_threshold-format-string.patch mm-page_owner-move-free_ts_nsec-output-to-free-section-in-__dump_page_owner.patch mm-page_owner-drop-redundant-page_owner-prefix-from-static-symbols.patch mm-page_owner-clamp-skip_buddy_pages-pfn-advance-at-max_order_nr_pages-boundary.patch mm-page_owner-use-memcg_data-snapshot-to-avoid-toctou-in-print_page_owner_memcg.patch