userfaultfd: wp: fault try one more time

For a swapin memory write fault, fault handler already retry once to
read the page in. userfaultfd can't do the retry again and fail. Give
another retry for userfaultfd in such case. gup isn't fixed yet, so will
return -EBUSY.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
27 files changed