From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 57E7226F440; Tue, 25 Mar 2025 12:39:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742906360; cv=none; b=TRePMxnUoggJx4i5ThkMGxGdZzidpGNkCjo5qH9dDGbcFFOsRbkpKiGM6vkGMok3mLjkFqwOq4OHe9Uwm547YCqNdeRh+6WNC/vG6bu9Jyf3fCjnOR70SF15Fsi93DqImV4uu8XD+aYMG3KTlRQvehTT0LQ1fRo5nV1wOVv8aus= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742906360; c=relaxed/simple; bh=EOIluI+kny8fB5FWGurRevjygR9iiBLGtbHuxvyPhUo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=o3vy7NXUdSo5bjtmu45HRVrnLLm+91fC0Y3yRK4Lk587GDGlckrnk7n2h7OmWkfjpruEAmqn+1GrU0iZGhAp3lO4MByRwWxthDrnE6qa82W+nVPX2H90Jb4E7Zv6/Fe6emRrL4p+/koA6G/J8rk7GAV74DwTEUejY9WVUgrSGeE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=J3IGNcJx; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="J3IGNcJx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DE43FC4CEE4; Tue, 25 Mar 2025 12:39:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1742906360; bh=EOIluI+kny8fB5FWGurRevjygR9iiBLGtbHuxvyPhUo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=J3IGNcJxyf+yfh/xsnvVI9f3Spa2LipdcM5zyZBnxhMXMg9OYmbKFqNbGzGy98F5a O7m7bskhWcQD5PbRhFLS55WW67kImL0baUhP97BPFOZnZ/bU4VYQiGQyBBPN69MeiR PdylnYoTvFOLm+yH06ULH38mIgURYZFWtKzzoKPQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Zi Yan , Liu Shixin , Hugh Dickins , "Matthew Wilcox (Oracle)" , Baolin Wang , Barry Song , Charan Teja Kalla , David Hildenbrand , Kefeng Wang , Lance Yang , Ryan Roberts , Andrew Morton Subject: [PATCH 6.12 076/116] mm/migrate: fix shmem xarray update during migration Date: Tue, 25 Mar 2025 08:22:43 -0400 Message-ID: <20250325122151.151590770@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250325122149.207086105@linuxfoundation.org> References: <20250325122149.207086105@linuxfoundation.org> User-Agent: quilt/0.68 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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Zi Yan commit 60cf233b585cdf1f3c5e52d1225606b86acd08b0 upstream. A shmem folio can be either in page cache or in swap cache, but not at the same time. Namely, once it is in swap cache, folio->mapping should be NULL, and the folio is no longer in a shmem mapping. In __folio_migrate_mapping(), to determine the number of xarray entries to update, folio_test_swapbacked() is used, but that conflates shmem in page cache case and shmem in swap cache case. It leads to xarray multi-index entry corruption, since it turns a sibling entry to a normal entry during xas_store() (see [1] for a userspace reproduction). Fix it by only using folio_test_swapcache() to determine whether xarray is storing swap cache entries or not to choose the right number of xarray entries to update. [1] https://lore.kernel.org/linux-mm/Z8idPCkaJW1IChjT@casper.infradead.org/ Note: In __split_huge_page(), folio_test_anon() && folio_test_swapcache() is used to get swap_cache address space, but that ignores the shmem folio in swap cache case. It could lead to NULL pointer dereferencing when a in-swap-cache shmem folio is split at __xa_store(), since !folio_test_anon() is true and folio->mapping is NULL. But fortunately, its caller split_huge_page_to_list_to_order() bails out early with EBUSY when folio->mapping is NULL. So no need to take care of it here. Link: https://lkml.kernel.org/r/20250305200403.2822855-1-ziy@nvidia.com Fixes: fc346d0a70a1 ("mm: migrate high-order folios in swap cache correctly") Signed-off-by: Zi Yan Reported-by: Liu Shixin Closes: https://lore.kernel.org/all/28546fb4-5210-bf75-16d6-43e1f8646080@huawei.com/ Suggested-by: Hugh Dickins Reviewed-by: Matthew Wilcox (Oracle) Reviewed-by: Baolin Wang Cc: Barry Song Cc: Charan Teja Kalla Cc: David Hildenbrand Cc: Hugh Dickins Cc: Kefeng Wang Cc: Lance Yang Cc: Ryan Roberts Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/migrate.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) --- a/mm/migrate.c +++ b/mm/migrate.c @@ -526,15 +526,13 @@ static int __folio_migrate_mapping(struc if (folio_test_anon(folio) && folio_test_large(folio)) mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON, 1); folio_ref_add(newfolio, nr); /* add cache reference */ - if (folio_test_swapbacked(folio)) { + if (folio_test_swapbacked(folio)) __folio_set_swapbacked(newfolio); - if (folio_test_swapcache(folio)) { - folio_set_swapcache(newfolio); - newfolio->private = folio_get_private(folio); - } + if (folio_test_swapcache(folio)) { + folio_set_swapcache(newfolio); + newfolio->private = folio_get_private(folio); entries = nr; } else { - VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio); entries = 1; }