mm/smaps: fix race between smaps_hugetlb_range and migration

In the Linux kernel, the following vulnerability has been resolved:

mm/smaps: fix race between smaps_hugetlb_range and migration

smaps_hugetlb_range() handles the pte without holdling ptl, and may be concurrenct with migration, leaing to BUG_ON in pfn_swap_entry_to_page(). The race is as follows.

smaps_hugetlb_range migrate_pages huge_ptep_get remove_migration_ptes folio_unlock pfn_swap_entry_folio BUG_ON

To fix it, hold ptl lock in smaps_hugetlb_range().