hulk inclusion
category: bugfix
bugzilla: 16080
CVE: NA
-------------------

the pointer new_pol can be NULL when mbind() mode arg was MPOL_DEFAULT,
so, before using new_pol, make sure it was not NULL.

Fixes: a72a680ff761 ("mm: Tag VMA with VM_CDM flag explicitly during mbind(MPOL_BIND) and page fault")
Signed-off-by: NLijun Fang <fanglijun3@huawei.com>
Reviewed-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>