Add some likely/unliklies, a for_each_cpu => for_each_cpu_online, and close
the sched_exit race.

From: Ingo Molnar <mingo@elte.hu>

  fix a typo in a previous patch breaking RT scheduling & interactivity.
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>