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 7CF6C259CAC; Wed, 5 Mar 2025 21:42:03 +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=1741210923; cv=none; b=alNw8aROdjY7K93A3pvLWL+Qk9zgfblcf4weZtfxCHzZmFJgnZ3qHmHunk/ygcRXQsgRhFfaiOSvLj9O3Ir7PmAEA9zlTj75mqFD5v2944A6c0sgwkyWZtnSHcKGh9W1Ayn+ktElgUly7jbrmgFvOb7Mtc0SzF7J7H2fgvSCpT4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741210923; c=relaxed/simple; bh=MEYlErtMNJGu33by+TzxsernoAlyBfFr0DR1qd9lK7s=; h=Date:To:From:Subject:Message-Id; b=gkwytEsEVdpHGeAxJVQytJ1pOxj0cc6BJczYjHWgHZNruKRN4JSp4egFGIOX+sRHQqeQDKrmbJ02NZMSGrQz6KHk3DgVdFSyAcr1AE0XN5Eky1oL88bW+bPhOhXJ7FhlzvXWd6/eQs0Cki8juP0KUir4W2MWKD/vfqZisO9wEpw= 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=BI+sRnJX; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="BI+sRnJX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BB55CC4CED1; Wed, 5 Mar 2025 21:42:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1741210922; bh=MEYlErtMNJGu33by+TzxsernoAlyBfFr0DR1qd9lK7s=; h=Date:To:From:Subject:From; b=BI+sRnJXarI7PG91EIILoliHTDaVJc7h3igxHYNINav3DhNukARL1XN9YBcNNrLgE KS1cVW4LH5CMBaC1uCdnsTRPALTXYcxUGZUx2BfcZVXFE5phER4KhR1lVv3S3QV79y bPq/ZJZzumo74VDDLyPZenbruc2tcmqbIDARx5Ec= Date: Wed, 05 Mar 2025 13:42:01 -0800 To: mm-commits@vger.kernel.org,willy@infradead.org,wangkefeng.wang@huawei.com,stable@vger.kernel.org,ryan.roberts@arm.com,quic_charante@quicinc.com,liushixin2@huawei.com,ioworker0@gmail.com,hughd@google.com,david@redhat.com,baolin.wang@linux.alibaba.com,baohua@kernel.org,ziy@nvidia.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-migrate-fix-shmem-xarray-update-during-migration.patch added to mm-hotfixes-unstable branch Message-Id: <20250305214202.BB55CC4CED1@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/migrate: fix shmem xarray update during migration has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-migrate-fix-shmem-xarray-update-during-migration.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-fix-shmem-xarray-update-during-migration.patch This patch will later appear in the mm-hotfixes-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 the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Zi Yan Subject: mm/migrate: fix shmem xarray update during migration Date: Wed, 5 Mar 2025 15:04:03 -0500 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") Reported-by: Liu Shixin Closes: https://lore.kernel.org/all/28546fb4-5210-bf75-16d6-43e1f8646080@huawei.com/ Suggested-by: Hugh Dickins Signed-off-by: Zi Yan Cc: Baolin Wang Cc: Barry Song Cc: Charan Teja Kalla Cc: David Hildenbrand Cc: Hugh Dickins Cc: Kefeng Wang Cc: Lance Yang Cc: Matthew Wilcow (Oracle) Cc: Ryan Roberts Cc: Zi Yan Cc: Signed-off-by: Andrew Morton --- mm/migrate.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) --- a/mm/migrate.c~mm-migrate-fix-shmem-xarray-update-during-migration +++ a/mm/migrate.c @@ -518,15 +518,13 @@ 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; } _ Patches currently in -mm which might be from ziy@nvidia.com are mm-migrate-fix-shmem-xarray-update-during-migration.patch selftests-mm-make-file-backed-thp-split-work-by-writing-pmd-size-data.patch mm-huge_memory-allow-split-shmem-large-folio-to-any-lower-order.patch selftests-mm-test-splitting-file-backed-thp-to-any-lower-order.patch