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...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Zi Yan ziy@nvidia.com Subject: mm/migrate: fix shmem xarray update during migration Date: Fri, 28 Feb 2025 12:49:53 -0500

Pagecache uses multi-index entries for large folio, so does shmem. Only swap cache still stores multiple entries for a single large folio. Commit fc346d0a70a1 ("mm: migrate high-order folios in swap cache correctly") fixed swap cache but got shmem wrong by storing multiple entries for a large shmem folio.

This results in a soft lockup as reported by Liu Shixin.

Fix it by storing a single entry for a shmem folio.

Link: https://lkml.kernel.org/r/20250228174953.2222831-1-ziy@nvidia.com Fixes: fc346d0a70a1 ("mm: migrate high-order folios in swap cache correctly") Signed-off-by: Zi Yan ziy@nvidia.com Reported-by: Liu Shixin liushixin2@huawei.com Closes: https://lore.kernel.org/all/28546fb4-5210-bf75-16d6-43e1f8646080@huawei.com/ Reviewed-by: Shivank Garg shivankg@amd.com Cc: Baolin Wang baolin.wang@linux.alibaba.com Cc: Barry Song baohua@kernel.org Cc: Charan Teja Kalla quic_charante@quicinc.com Cc: David Hildenbrand david@redhat.com Cc: Hugh Dickens hughd@google.com Cc: Kefeng Wang wangkefeng.wang@huawei.com Cc: Lance Yang ioworker0@gmail.com Cc: Matthew Wilcow (Oracle) willy@infradead.org Cc: Ryan Roberts ryan.roberts@arm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/migrate.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/mm/migrate.c~mm-migrate-fix-shmem-xarray-update-during-migration +++ a/mm/migrate.c @@ -524,7 +524,11 @@ static int __folio_migrate_mapping(struc folio_set_swapcache(newfolio); newfolio->private = folio_get_private(folio); } - entries = nr; + /* shmem uses high-order entry */ + if (!folio_test_anon(folio)) + entries = 1; + else + 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 xarray-add-xas_try_split-to-split-a-multi-index-entry.patch mm-huge_memory-add-two-new-not-yet-used-functions-for-folio_split.patch mm-huge_memory-move-folio-split-common-code-to-__folio_split.patch mm-huge_memory-add-buddy-allocator-like-non-uniform-folio_split.patch mm-huge_memory-remove-the-old-unused-__split_huge_page.patch mm-huge_memory-add-folio_split-to-debugfs-testing-interface.patch mm-truncate-use-buddy-allocator-like-folio-split-for-truncate-operation.patch mm-truncate-use-buddy-allocator-like-folio-split-for-truncate-operation-fix.patch selftests-mm-add-tests-for-folio_split-buddy-allocator-like-split.patch mm-filemap-use-xas_try_split-in-__filemap_add_folio.patch mm-shmem-use-xas_try_split-in-shmem_split_large_entry.patch