locking, sched: Give waitqueue spinlocks their own lockdep classes

locking, sched: Give waitqueue spinlocks their own lockdep classes

Give waitqueue spinlocks their own lockdep classes when they
are initialised from init_waitqueue_head().  This means that
struct wait_queue::func functions can operate other waitqueues.

This is used by CacheFiles to catch the page from a backing fs
being unlocked and to wake up another thread to take a copy of
it.

Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: David Howells <[email protected]>
Tested-by: Takashi Iwai <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
LKML-Reference: <20090810113305[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>