mm/migrate.c: pair unlock_page() and lock_page() when migrating huge pages

Avoid unlocking and unlocked page if we failed to lock it.
Signed-off-by: Hillf Danton <dhillf@gmail.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/migrate.c

@@ -871,9 +871,9 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 
 	if (anon_vma)
 		put_anon_vma(anon_vma);
-out:
 	unlock_page(hpage);
 
+out:
 	if (rc != -EAGAIN) {
 		list_del(&hpage->lru);
 		put_page(hpage);