mm: fix process accidentally killed by mce because of huge page migration

Based on c8721bbb upstream, but only the
bugfix portion pulled out.

Hi Naoya or Greg,

We found a bug in 3.10.x.
The problem is that we accidentally have a hwpoisoned hugepage in free
hugepage list. It could happend in the the following scenario:

        process A                           process B

  migrate_huge_page
  put_page (old hugepage)
    linked to free hugepage list
                                     hugetlb_fault
                                       hugetlb_no_page
                                         alloc_huge_page
                                           dequeue_huge_page_vma
                                             dequeue_huge_page_node
                                               (steal hwpoisoned hugepage)
  set_page_hwpoison_huge_page
  dequeue_hwpoisoned_huge_page
    (fail to dequeue)

I tested this bug, one process keeps allocating huge page, and I 
use sysfs interface to soft offline a huge page, then received:
"MCE: Killing UCP:2717 due to hardware memory corruption fault at 8200034"

Upstream kernel is free from this bug because of these two commits:

f15bdfa8
mm/memory-failure.c: fix memory leak in successful soft offlining

c8721bbb
mm: memory-hotplug: enable memory hotplug to handle hugepage

The first one, although the problem is about memory leak, this patch
moves unset_migratetype_isolate(), which is important to avoid the race.
The latter is not a bug fix and it's too big, so I rewrite a small one.

The following patch can fix this bug.(please apply f15bdfa8 first)

Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>