[PATCH] lockdep: annotate futex

Teach special (recursive) locking code to the lock validator.  Introduces
double_lock_hb() to unify double- hash-bucket-lock taking.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>