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 <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Yang Shi <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Cc: Jerome Glisse <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Bharata B Rao <[email protected]>
Cc: Ben Skeggs <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: <[email protected]>	[4.14+]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions