On 2 Sep 2020, at 12:58, Ralph Campbell wrote:
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.
Signed-off-by: Ralph Campbell rcampbell@nvidia.com
Thanks for the fix. You can add Reviewed-by: Zi Yan ziy@nvidia.com
I think you also want to add the Fixes tag and cc stable.
Fixes 84c3fc4e9c56 (“mm: thp: check pmd migration entry in common path”) cc: stable@vger.kernel.org # 4.14+
mm/huge_memory.c | 42 +++++++++++++++++++++++------------------- 1 file changed, 23 insertions(+), 19 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 2a468a4acb0a..606d712d9505 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2023,7 +2023,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, 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
@@ -2117,30 +2117,34 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, 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);
-- 2.20.1
— Best Regards, Yan Zi