mm/huge_memory.c: deposit page table when copying a PMD migration entry

mm/huge_memory.c: deposit page table when copying a PMD migration entry

We need to deposit pre-allocated PTE page table when a PMD migration
entry is copied in copy_huge_pmd().  Otherwise, we will leak the
pre-allocated page and cause a NULL pointer dereference later in
zap_huge_pmd().

The missing counters during PMD migration entry copy process are added
as well.

The bug report is here: https://lkml.org/lkml/2017/10/29/214

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 84c3fc4e9c563 ("mm: thp: check pmd migration entry in common path")
Signed-off-by: Zi Yan <[email protected]>
Reported-by: Fengguang Wu <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>