Commit ec0abae6 authored Sep 18, 2020 by Ralph Campbell Committed by Linus Torvalds Sep 19, 2020

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: 84c3fc4e ("mm: thp: check pmd migration entry in common path")
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Bharata B Rao <bharata@linux.ibm.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: <stable@vger.kernel.org>	[4.14+]
Link: https://lkml.kernel.org/r/20200903183140.19055-1-rcampbell@nvidia.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent b0399092

mm/huge_memory.c

+23 −19

Original line number	Diff line number	Diff line
		@@ -2022,7 +2022,7 @@ 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
		@@ -2116,15 +2116,18 @@ 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);
		if (!pmd_migration)
		atomic_inc(&page[i]._mapcount);
		pte_unmap(pte);
		}

		if (!pmd_migration) {
		/*
		* Set PG_double_map before dropping compound_mapcount to avoid
		* false-negative page_mapped().
		*/
		if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
		if (compound_mapcount(page) > 1 &&
		!TestSetPageDoubleMap(page)) {
		for (i = 0; i < HPAGE_PMD_NR; i++)
		atomic_inc(&page[i]._mapcount);
		}
		@@ -2140,6 +2143,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct vma, pmd_t pmd,
		}
		}
		unlock_page_memcg(page);
		}

		smp_wmb(); /* make pte visible before pmd */
		pmd_populate(mm, pmd, pgtable);

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