userfaultfd: replace ENOSPC with ESRCH in case mm has gone during copy/zeropage

userfaultfd: replace ENOSPC with ESRCH in case mm has gone during copy/zeropage

When the process exit races with outstanding mcopy_atomic, it would be
better to return ESRCH error.  When such race occurs the process and
it's mm are going away and returning "no such process" to the uffd
monitor seems better fit than ENOSPC.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Mike Rapoport <[email protected]>
Suggested-by: Michal Hocko <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: "Dr. David Alan Gilbert" <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Mike Kravetz <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>