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 7245238A70A for ; Tue, 14 Jul 2026 03:11:01 +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=1783998662; cv=none; b=L6Tiyh0mZnTmfmbbCPxlQkT8Us+euy57CAP+7z8O41ittRngM+gYB6ojyBc30GQfcMTez09C163juEDU2Xf4/LHnmjIBFsTT9KLeydUpgmdVwwMMmkNFKYa5FcF0h34aa/Om5U4HIB1+4cbWikkfQZM1v69LZg7wHGaLadW+XBc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783998662; c=relaxed/simple; bh=GhO5dWI5FmdB1zJnSvlVrnMTqe9hOYe1HXhJQy3Zwkc=; h=Date:To:From:Subject:Message-Id; b=O/RndQtk6oHDzB6g2XMsOKOsYRt2MkUG9UfUHOmimQESgklw1P6cczdsq8/6sDZhh1JOcTRaPC57POMDT/rgVP43av/jAcu/XXNJ+L3p4GKJPJLGSd20guiOz3tuTXe1/jOJx1hSGM7Ex2+EMRXFEoQvDAnNcyGDvNdVZYQri1c= 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=CXeuxfBh; 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="CXeuxfBh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 415061F000E9; Tue, 14 Jul 2026 03:11:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1783998661; bh=nFMB5fSyn86+6ZOrJzt9OUaTmH1wNguHYukhTXUU1iI=; h=Date:To:From:Subject; b=CXeuxfBhINpKmCR6N0ReDdBN0WPzeW3eHq+VWeELDkxSiKz31EQGg4DckSyzYcGT8 woKnbn46tSpdQfLqUnErMc3FcYM5KBQzAVywsKCknNFiL3smwDgZycKcK165JmHWks nTe1Kh0PAiQMDQ2BsuGoe6fF6KbWXfFHP0OOAJNA= Date: Mon, 13 Jul 2026 20:11:00 -0700 To: mm-commits@vger.kernel.org,ye.liu@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: [to-be-updated] mm-page_owner-use-memcg_data-snapshot-instead-of-pagememcgkmem-to-avoid-toctou-vm_bug_on.patch removed from -mm tree Message-Id: <20260714031101.415061F000E9@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/page_owner: use memcg_data snapshot instead of PageMemcgKmem() to avoid TOCTOU VM_BUG_ON has been removed from the -mm tree. Its filename was mm-page_owner-use-memcg_data-snapshot-instead-of-pagememcgkmem-to-avoid-toctou-vm_bug_on.patch This patch was dropped because an updated version will be issued ------------------------------------------------------ From: Ye Liu Subject: mm/page_owner: use memcg_data snapshot instead of PageMemcgKmem() to avoid TOCTOU VM_BUG_ON Date: Wed, 1 Jul 2026 14:10:52 +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, at the end it calls PageMemcgKmem(page) which internally calls folio_memcg_kmem() — and that function re-reads folio->memcg_data and page->compound_head locklessly, 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 this final call, the VM_BUG_ON assertions can fire on debug builds (CONFIG_DEBUG_VM=y), causing a kernel panic. Fix by reusing the memcg_data snapshot already taken at function entry instead of calling PageMemcgKmem(), which is semantically equivalent: PageMemcgKmem()->folio_memcg_kmem()->folio->memcg_data & MEMCG_DATA_KMEM. This avoids both the TOCTOU window and the assertions entirely. Link: https://lore.kernel.org/20260701061101.344679-10-ye.liu@linux.dev Signed-off-by: Ye Liu Reviewed-by: Vlastimil Babka (SUSE) Reviewed-by: Zi Yan Cc: Brendan Jackman Cc: Johannes Weiner Cc: Michal Hocko Cc: Suren Baghdasaryan Cc: Lorenzo Stoakes Signed-off-by: Andrew Morton --- mm/page_owner.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/page_owner.c~mm-page_owner-use-memcg_data-snapshot-instead-of-pagememcgkmem-to-avoid-toctou-vm_bug_on +++ a/mm/page_owner.c @@ -561,7 +561,7 @@ 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