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 0DF173A6F0A; Fri, 7 Aug 2026 15:42:53 +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=1786117374; cv=none; b=iFUEghlYxbinV5WcaYqNU4wC9MFaGFfLKlZr0WGpvqhAxRn+ifh8wPRgEh42/KnptBGDUNiol9Mre4fa3USzjWILCh5jpSL4n9c8ERzyT+wagkX5ctESDwWyH9jz0buvQruqHXyNPBK8lkWD5DKZjs5CEQrVaehdwgYWn8haaD8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786117374; c=relaxed/simple; bh=WbFpEDXB4aOv0VkabwtRM0Zgx508Woq2oABK6JSHPs0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=HZ45zgPNI4dwFWZ4cXwVsMwWbJJqB2C15lJMOZmuwCzxscs+8IYO1mM+cHxpDE64svDpNhpulZdF0Byi6wh/8AahgYLRmfTCDMo9X4vibFjFxkq45FterC3FD2HuVjJ9gbABdE3q6T+PUp4TQruJ53JxleJcZWO5W8ZKmhdWBKE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=bxicBfPr; 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="bxicBfPr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 411621F000E9; Fri, 7 Aug 2026 15:42:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786117372; bh=60Xe/lWoHBD882eiScpkin0eGNGw9sFfBXrt6cOq9jE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bxicBfPrDGwK1X+XtP3KJdvEMK30yZhFkuNoA+gEUZEVQLgNgavcyW1ALrvPyIXhX JwVO3f3LQGzApAu9YX3vvnAr7DkC4q4LdjEzXmm/GwU8Ug9XtxtVbpN/muBuuTbuSS oYgRkJUQPdwxRZd89GxWPkX7tyJasjd6j2ei4w58= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Kiryl Shutsemau (Meta)" , Hao Zhang , "David Hildenbrand (Arm)" , Zi Yan , Baolin Wang , Miaohe Lin , Barry Song , Dev Jain , Lance Yang , "Liam R. Howlett" , Lorenzo Stoakes , Naoya Horiguchi , Nico Pache , Ryan Roberts , Andrew Morton Subject: [PATCH 7.1 295/438] mm/huge_memory: unlock i_mmap_rwsem before releasing after-split folios Date: Fri, 7 Aug 2026 16:38:11 +0200 Message-ID: <20260807143434.262508396@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260807143428.008222056@linuxfoundation.org> References: <20260807143428.008222056@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kiryl Shutsemau (Meta) commit e923bd21058ea02fd0dcd3549d151d143fd036e5 upstream. __folio_split() keeps dereferencing the mapping after the split: shmem_uncharge(mapping->host) and remap_page() while the folios are still frozen/locked, and i_mmap_unlock_read(mapping) at the very end, after the after-split folios have been unlocked and freed. Nothing holds an inode reference across that. The split relies on @folio -- which the beyond-EOF drop loop never removes, as it starts at folio_next(folio) -- staying locked and in the page cache to hold off eviction. But the unlock loop unlocks @folio before i_mmap_unlock_read() runs. If the caller's @lock_at is a tail beyond EOF, as memory_failure() passes when splitting a poisoned tail of a shmem THP that reaches past i_size during truncation, it too is gone from the page cache; so once @folio is unlocked no locked, in-cache folio pins the inode, and a concurrent final iput() can evict and RCU-free it before i_mmap_unlock_read() touches i_mmap_rwsem: BUG: KASAN: slab-use-after-free in __up_read+0x634/0x790 i_mmap_unlock_read include/linux/fs.h:537 [inline] __folio_split+0x732/0x1640 mm/huge_memory.c:4100 try_to_split_thp_page+0xab/0x390 mm/memory-failure.c:1675 memory_failure+0x1394/0x26e0 mm/memory-failure.c:2470 Freed by task 4601: shmem_free_in_core_inode+0x54/0xb0 mm/shmem.c:5177 evict+0x57f/0xac0 fs/inode.c:870 Do every mapping dereference while @folio still pins the inode: drop i_mmap_rwsem right after remap_page(), before the loop that unlocks and frees the after-split folios, and clear @mapping so the exit path does not unlock it again. shmem_uncharge() and remap_page() already run before that point, so after this nothing past the unlock loop touches the inode or the mapping. This is now a rule the split depends on, alongside keeping @folio frozen until the page cache is updated: no inode or mapping dereference once the after-split folios start being unlocked. Link: https://lore.kernel.org/20260716095424.471052-1-kirill@shutemov.name Fixes: baa355fd3314 ("thp: file pages support for split_huge_page()") Signed-off-by: Kiryl Shutsemau (Meta) Reported-by: Hao Zhang Closes: https://lore.kernel.org/linux-mm/20260710071344.GA106129@zh-pc Co-developed-by: Hao Zhang Signed-off-by: Hao Zhang Acked-by: David Hildenbrand (Arm) Reviewed-by: Zi Yan Reviewed-by: Baolin Wang Reviewed-by: Miaohe Lin Cc: Baolin Wang Cc: Barry Song Cc: Dev Jain Cc: Lance Yang Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Naoya Horiguchi Cc: Nico Pache Cc: Ryan Roberts Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/huge_memory.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -4189,6 +4189,18 @@ fail: remap_page(folio, 1 << old_order, ttu_flags); /* + * Drop the mapping while the inode is still pinned. @folio stays + * locked and present in the page cache until the loop below, so + * eviction cannot free the inode yet; @lock_at is not enough, it may + * be a tail beyond EOF that the split already dropped from the page + * cache. Nothing past this point may touch the inode or the mapping. + */ + if (mapping) { + i_mmap_unlock_read(mapping); + mapping = NULL; + } + + /* * Unlock all after-split folios except the one containing * @lock_at page. If @folio is not split, it will be kept locked. */