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 E48234AA008 for ; Thu, 3 Sep 2026 12:46:15 +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=1788439577; cv=none; b=dTkVxuAGObDKXbxP/EsW+MUcDmxuDuFYBp6qPv8Ie1VdkX4NDkNtW6mEiyy4Nbwcawv4NVAHKicmk86/Wdk1gJ1+K6F76tFjOKJOBpKJTctHA9hrtkaUS84ej52hmqkfTLfmf+tt3WvIKIPpOr5K1Ax4FXOMT+02xojw2a3hiJg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788439577; c=relaxed/simple; bh=vuguN106UArREAP71JLHvYShbqIp12Y/i1rN3VLShQo=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=S69FTvKJErc+hMDS05+QwbczkvVjd2gPQKhB+KTE43mtMbVEePLmaBBiU+rfWgz8XJ7clC0oqr792J+2lMhm0Dk0313dvrK1+OJCNkmO7zOivKU+KEvKJ6PJlPQAUkAe5hbfuJbVETWahK0xqBtw0XPEKOgpO7vK2BCK6dE7fPs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=To4Wp5gv; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="To4Wp5gv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 489431F000E9; Thu, 3 Sep 2026 12:46:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788439575; bh=KUatLNJlis5GWq34YG4pRJJdDJJHdD9Ek+nj301ikIk=; h=Subject:To:Cc:From:Date; b=To4Wp5gvRC/Fp33p9kkDFVVlBl3vWIGfG9Tg4pXpnTTl15m1qVpcl3vMsWmm88cUx S8ShwfBYAiu3PlreWkaEOKSGVrQmRGACbKr/rty+RRDd6xciFuYIbUH5T9YuhbeNkL P6Yd1ePh2gGyB1eIColTaS4Qn6M8kv12AYkTL0bU= Subject: FAILED: patch "[PATCH] mm/page_owner: use memcg_data snapshot to avoid TOCTOU in" failed to apply to 6.6-stable tree To: ye.liu@linux.dev,akpm@linux-foundation.org,david@kernel.org,hannes@cmpxchg.org,jackmanb@google.com,ljs@kernel.org,mhocko@suse.com,sashiko-bot@kernel.org,stable@vger.kernel.org,surenb@google.com,vbabka@kernel.org,ziy@nvidia.com Cc: From: Date: Thu, 03 Sep 2026 12:49:14 +0200 Message-ID: <2026090314-dayroom-oblong-b702@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 90f095b816e25c6a9e4446d299bac5007fdcb3df # git commit -s git send-email --to '' --in-reply-to '2026090314-dayroom-oblong-b702@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 90f095b816e25c6a9e4446d299bac5007fdcb3df Mon Sep 17 00:00:00 2001 From: Ye Liu Date: Tue, 14 Jul 2026 09:51:08 +0800 Subject: [PATCH] mm/page_owner: use memcg_data snapshot to avoid TOCTOU in print_page_owner_memcg() print_page_owner_memcg() reads page->memcg_data via READ_ONCE() at the start to guard against tail pages and NULL data. However, it later re-reads page->memcg_data locklessly in two places: 1: page_memcg_check(page) 2: PageMemcgKmem(page) (via folio_memcg_kmem(), which includes VM_BUG_ON assertions for tail pages and MEMCG_DATA_OBJEXTS) If the page is concurrently freed and reallocated as a THP tail page or slab page between these calls, the VM_BUG_ON assertions can trigger on CONFIG_DEBUG_VM=y builds, crashing the kernel. Fix both TOCTOU issues by using the memcg_data snapshot throughout. Link: https://lore.kernel.org/20260714015117.78351-10-ye.liu@linux.dev Fixes: fcf8935832b8 ("mm/page_owner: print memcg information") Signed-off-by: Ye Liu Reported-by: Sashiko Reviewed-by: Zi Yan Reviewed-by: Vlastimil Babka (SUSE) Cc: Brendan Jackman Cc: Johannes Weiner Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Suren Baghdasaryan Cc: David Hildenbrand (Arm) Cc: Signed-off-by: Andrew Morton diff --git a/mm/page_owner.c b/mm/page_owner.c index 2e3880053a34..e18512a49e38 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -540,6 +540,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret, 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(char *kbuf, size_t count, int ret, 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(char *kbuf, size_t count, int ret, 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: