mm/hugetlb: check for pte NULL pointer in __page_check_address()

mm/hugetlb: check for pte NULL pointer in __page_check_address()

commit 98398c32f6687ee1e1f3ae084effb4b75adb0747 upstream.

In __page_check_address(), if address's pud is not present,
huge_pte_offset() will return NULL, we should check the return value.

Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: qiuxishi <qiuxishi@huawei.com>
Cc: Hanjun Guo <guohanjun@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>