"case 0" in free_pid() assumes that disable_pid_allocation() should
clear PIDNS_HASH_ADDING before the last pid goes away.

However this doesn't happen if the first fork() fails to create the
child reaper which should call disable_pid_allocation().
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Reviewed-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>