This introduces the following 3 new locking primitives:

  spin_can_lock(lock)
  read_can_lock(lock)
  write_can_lock(lock)

which are a nonintrusive test to check whether the real (intrusive)
trylock op would succeed or not.  Semantics and naming is completely
symmetric to the trylock counterpart.

Architectures that want to support PREEMPT will need to add these
definitions.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>