mm/migrate.c: make putback_movable_page() static

Patch series "Cleanup and fixup for mm/migrate.c", v3.

This series contains cleanups to remove unnecessary VM_BUG_ON_PAGE and rc
!= MIGRATEPAGE_SUCCESS check.  Also use helper function to remove some
duplicated codes.  What's more, this fixes potential deadlock in NUMA
balancing shared exec THP case and so on.  More details can be found in
the respective changelogs.

This patch (of 5):

The putback_movable_page() is just called by putback_movable_pages() and
we know the page is locked and both PageMovable() and PageIsolated() is
checked right before calling putback_movable_page().  So we make it static
and remove all the 3 VM_BUG_ON_PAGE().

Link: https://lkml.kernel.org/r/20210325131524.48181-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20210325131524.48181-2-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>