The patch titled
Subject: mm/thp: refix __split_huge_pmd_locked() for migration PMD
has been added to the -mm tree. Its filename is
mm-thp-refix-__split_huge_pmd_locked-for-migration-pmd.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-thp-refix-__split_huge_pmd_locked-for-migration-pmd.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-refix-__split_huge_pmd_locked-for-migration-pmd.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
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 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@xxxxxxxxxx
Fixes: ec0abae6dcdf ("mm/thp: fix __split_huge_pmd_locked() for migration PMD")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx are
memfd-fix-f_seal_write-after-shmem-huge-page-allocated.patch
tmpfs-support-for-file-creation-time-fix.patch
mm-thp-refix-__split_huge_pmd_locked-for-migration-pmd.patch
mm-thp-fix-nr_file_mapped-accounting-in-page__file_rmap.patch
mm-thp-clearpagedoublemap-in-first-page_add_file_rmap.patch
