kernel - Fix MP race in sysv semaphore code

kernel - Fix MP race in sysv semaphore code

* Fix a serious MP race in the sysv semaphore code due to a lack of
  protection of the semu* global structures.

* The race occurs during semaphore allocation and deallocation vs ANY
  exiting process (even if it does not use semaphores), potentially
  leading to a live-lock in the semu_list scan code.

  The live-lock will prevent the cpu it occurs on from being able to
  switch to another kernel or user thread.  In the sample case it
  stopped pagedaemon from running, creating a backlog in the I/O
  subsystem which locked the computer up.

Reported-by: Peter Avalos