The patch titled
Subject: mm/thp: fix __split_huge_pmd_locked() for migration PMD
has been added to the -mm tree. Its filename is
mm-thp-fix-__split_huge_pmd_locked-for-migration-pmd.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-thp-fix-__split_huge_pmd_locked-for-migration-pmd.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-fix-__split_huge_pmd_locked-for-migration-pmd.patch
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------------------------------------------------------
From: Ralph Campbell <rcampbell@xxxxxxxxxx>
Subject: mm/thp: fix __split_huge_pmd_locked() for migration PMD
A migrating transparent huge page has to already be unmapped. Otherwise,
the page could be modified while it is being copied to a new page and data
could be lost. The function __split_huge_pmd() checks for a PMD migration
entry before calling __split_huge_pmd_locked() leading one to think that
__split_huge_pmd_locked() can handle splitting a migrating PMD.
However, the code always increments the page->_mapcount and adjusts the
memory control group accounting assuming the page is mapped.
Also, if the PMD entry is a migration PMD entry, the call to
is_huge_zero_pmd(*pmd) is incorrect because it calls pmd_pfn(pmd) instead
of migration_entry_to_pfn(pmd_to_swp_entry(pmd)). Fix these problems by
checking for a PMD migration entry.
Link: https://lkml.kernel.org/r/20200903183140.19055-1-rcampbell@xxxxxxxxxx
Fixes: 84c3fc4e9c56 ("mm: thp: check pmd migration entry in common path")
Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Bharata B Rao <bharata@xxxxxxxxxxxxx>
Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.14+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 42 +++++++++++++++++++++++-------------------
1 file changed, 23 insertions(+), 19 deletions(-)
--- a/mm/huge_memory.c~mm-thp-fix-__split_huge_pmd_locked-for-migration-pmd
+++ a/mm/huge_memory.c
@@ -2021,7 +2021,7 @@ static void __split_huge_pmd_locked(stru
put_page(page);
add_mm_counter(mm, mm_counter_file(page), -HPAGE_PMD_NR);
return;
- } else if (is_huge_zero_pmd(*pmd)) {
+ } else if (pmd_trans_huge(*pmd) && is_huge_zero_pmd(*pmd)) {
/*
* FIXME: Do we want to invalidate secondary mmu by calling
* mmu_notifier_invalidate_range() see comments below inside
@@ -2115,30 +2115,34 @@ static void __split_huge_pmd_locked(stru
pte = pte_offset_map(&_pmd, addr);
BUG_ON(!pte_none(*pte));
set_pte_at(mm, addr, pte, entry);
- atomic_inc(&page[i]._mapcount);
- pte_unmap(pte);
- }
-
- /*
- * Set PG_double_map before dropping compound_mapcount to avoid
- * false-negative page_mapped().
- */
- if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
- for (i = 0; i < HPAGE_PMD_NR; i++)
+ if (!pmd_migration)
atomic_inc(&page[i]._mapcount);
+ pte_unmap(pte);
}
- lock_page_memcg(page);
- if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
- /* Last compound_mapcount is gone. */
- __dec_lruvec_page_state(page, NR_ANON_THPS);
- if (TestClearPageDoubleMap(page)) {
- /* No need in mapcount reference anymore */
+ if (!pmd_migration) {
+ /*
+ * Set PG_double_map before dropping compound_mapcount to avoid
+ * false-negative page_mapped().
+ */
+ if (compound_mapcount(page) > 1 &&
+ !TestSetPageDoubleMap(page)) {
for (i = 0; i < HPAGE_PMD_NR; i++)
- atomic_dec(&page[i]._mapcount);
+ atomic_inc(&page[i]._mapcount);
+ }
+
+ lock_page_memcg(page);
+ if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
+ /* Last compound_mapcount is gone. */
+ __dec_lruvec_page_state(page, NR_ANON_THPS);
+ if (TestClearPageDoubleMap(page)) {
+ /* No need in mapcount reference anymore */
+ for (i = 0; i < HPAGE_PMD_NR; i++)
+ atomic_dec(&page[i]._mapcount);
+ }
}
+ unlock_page_memcg(page);
}
- unlock_page_memcg(page);
smp_wmb(); /* make pte visible before pmd */
pmd_populate(mm, pmd, pgtable);
_
Patches currently in -mm which might be from rcampbell@xxxxxxxxxx are
mm-thp-fix-__split_huge_pmd_locked-for-migration-pmd.patch
mm-test-use-the-new-skip-macro.patch
mm-migrate-remove-cpages-in-migrate_vma_finalize.patch
mm-migrate-remove-obsolete-comment-about-device-public.patch
