userfaultfd: hugetlbfs: reserve count on error in __mcopy_atomic_hugetlb

userfaultfd: hugetlbfs: reserve count on error in __mcopy_atomic_hugetlb

Orabug: 21685254

If __mcopy_atomic_hugetlb exits with an error, put_page will be called if
a huge page was allocated and needs to be freed.  If a reservation was
associated with the huge page, the PagePrivate flag will be set.  Clear
PagePrivate before calling put_page/free_huge_page so that the global
reservation count is not incremented.

Link: http://lkml.kernel.org/r/20161216144821.5183-26-aarcange@redhat.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from linux-next next-20170117
 commit afcc2616d4284859d8f70bbdfa6c9ca92fbb08ed)
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Dhaval Giani <dhaval.giani@oracle.com>
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>