[merged] mm-thp-refix-__split_huge_pmd_locked-for-migration-pmd.patch removed from -mm tree

[merged] mm-thp-refix-__split_huge_pmd_locked-for-migration-pmd.patch removed from -mm tree

[Andrew Morton]

The patch titled
     Subject: mm/thp: refix __split_huge_pmd_locked() for migration PMD
has been removed from the -mm tree.  Its filename was
     mm-thp-refix-__split_huge_pmd_locked-for-migration-pmd.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: mm/thp: refix __split_huge_pmd_locked() for migration PMD

Migration entries do not contribute to a page's reference count: move
__split_huge_pmd_locked()'s page_ref_add() into pmd_migration's else block
(along with the page_count() check - a page is quite likely to have
reference count frozen to 0 when a migration entry is found).

This will fix a very rare anonymous memory leak, after a split_huge_pmd()
raced with an anon split_huge_page() or an anon THP migrate_pages(): since
the wrongly raised refcount stopped the page (perhaps small, perhaps huge,
depending on when the race hit) from ever being freed.  At first I thought
there were worse risks, from prematurely unfreezing a frozen page: but now
think that would only affect page cache pages, which do not come this way
(except for anonymous pages in swap cache, perhaps).

Link: https://lkml.kernel.org/r/84792468-f512-e48f-378c-e34c3641e97@google.com
Fixes: ec0abae6dcdf ("mm/thp: fix __split_huge_pmd_locked() for migration PMD")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/huge_memory.c~mm-thp-refix-__split_huge_pmd_locked-for-migration-pmd
+++ a/mm/huge_memory.c
@@ -2055,9 +2055,9 @@ static void __split_huge_pmd_locked(stru
 		young = pmd_young(old_pmd);
 		soft_dirty = pmd_soft_dirty(old_pmd);
 		uffd_wp = pmd_uffd_wp(old_pmd);
+		VM_BUG_ON_PAGE(!page_count(page), page);
+		page_ref_add(page, HPAGE_PMD_NR - 1);
 	}
-	VM_BUG_ON_PAGE(!page_count(page), page);
-	page_ref_add(page, HPAGE_PMD_NR - 1);
 
 	/*
 	 * Withdraw the table only after we mark the pmd entry invalid.
_

Patches currently in -mm which might be from hughd@google.com are

mm-delete-__clearpagewaiters.patch
mm-filemap_unaccount_folio-large-skip-mapcount-fixup.patch
mm-thp-fix-nr_file_mapped-accounting-in-page__file_rmap.patch
mm-warn-on-deleting-redirtied-only-if-accounted.patch
mm-unmap_mapping_range_tree-with-i_mmap_rwsem-shared.patch