mm: rmap: call page_check_address() with sync enabled to avoid racy check

mm: rmap: call page_check_address() with sync enabled to avoid racy check

The previous patch addresses the race between split_huge_pmd_address()
and someone changing the pmd.  The fix is only for splitting of normal
thp (i.e.  pmd-mapped thp,) and for splitting of pte-mapped thp there
still is the similar race.

For splitting pte-mapped thp, the pte's conversion is done by
try_to_unmap_one(TTU_MIGRATION).  This function checks
page_check_address() to get the target pte, but it can return NULL under
some race, leading to VM_BUG_ON() in freeze_page().  Fortunately,
page_check_address() already has an argument to decide whether we do a
quick/racy check or not, so let's flip it when called from
freeze_page().

Link: http://lkml.kernel.org/r/1466990929-7452-2-git-send-email-n-horiguchi@ah.jp.nec.com
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: 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>