On 21 Sep 2020, at 14:27, Zi Yan wrote:
> From: Zi Yan <ziy@xxxxxxxxxx>
>
> For 4.19.
It applies to v5.4.y too.
>
> [Upstream commitid ec0abae6dcdf7ef88607c869bf35a4b63ce1b370]
>
> From: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Date: Fri, 18 Sep 2020 21:20:24 -0700
> Subject: [PATCH] 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.
>
> Fixes: 84c3fc4e9c56 ("mm: thp: check pmd migration entry in common path")
> Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> 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+]
> Link: https://lkml.kernel.org/r/20200903183140.19055-1-rcampbell@xxxxxxxxxx
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> ---
> mm/huge_memory.c | 37 ++++++++++++++++++++-----------------
> 1 file changed, 20 insertions(+), 17 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 1443ae6fee9b..811fb2477ecd 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2145,7 +2145,7 @@ 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
> @@ -2233,26 +2233,29 @@ 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);
> }
>
> - if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
> - /* Last compound_mapcount is gone. */
> - __dec_node_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);
> + }
> +
> + if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
> + /* Last compound_mapcount is gone. */
> + __dec_node_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);
> + }
> }
> }
>
> --
> 2.28.0
—
Best Regards,
Yan Zi
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