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
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------------------------------------------------------
From: Zi Yan <ziy@xxxxxxxxxx>
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@xxxxxxxxxx
Fixes: fc346d0a70a1 ("mm: migrate high-order folios in swap cache correctly")
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Reported-by: Liu Shixin <liushixin2@xxxxxxxxxx>
Closes: https://lore.kernel.org/all/28546fb4-5210-bf75-16d6-43e1f8646080@xxxxxxxxxx/
Reviewed-by: Shivank Garg <shivankg@xxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickens <hughd@xxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Lance Yang <ioworker0@xxxxxxxxx>
Cc: Matthew Wilcow (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx 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
