locking/rtmutex: Prevent lockdep false positive with PI futexes

void __sched rt_mutex_init_proxy_locked(struct rt_mutex_base *lock,

					struct task_struct *proxy_owner)

{

	static struct lock_class_key pi_futex_key;

	__rt_mutex_base_init(lock);

	/*

	 * On PREEMPT_RT the futex hashbucket spinlock becomes 'sleeping'

	 * and rtmutex based. That causes a lockdep false positive, because

	 * some of the futex functions invoke spin_unlock(&hb->lock) with

	 * the wait_lock of the rtmutex associated to the pi_futex held.

	 * spin_unlock() in turn takes wait_lock of the rtmutex on which

	 * the spinlock is based, which makes lockdep notice a lock

	 * recursion. Give the futex/rtmutex wait_lock a separate key.

	 */

	lockdep_set_class(&lock->wait_lock, &pi_futex_key);

	rt_mutex_set_owner(lock, proxy_owner);

}