futex: Fix errors in nested key ref-counting

futex_wait() is leaking key references due to futex_wait_setup()
acquiring an additional reference via the queue_lock() routine. The
nested key ref-counting has been masking bugs and complicating code
analysis. queue_lock() is only called with a previously ref-counted
key, so remove the additional ref-counting from the queue_(un)lock()
functions.

Also futex_wait_requeue_pi() drops one key reference too many in
unqueue_me_pi(). Remove the key reference handling from
unqueue_me_pi(). This was paired with a queue_lock() in
futex_lock_pi(), so the count remains unchanged.

Document remaining nested key ref-counting sites.

Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Reported-and-tested-by: Matthieu Fertré<matthieu.fertre@kerlabs.com>
Reported-by: Louis Rilling<louis.rilling@kerlabs.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
LKML-Reference: <4CBB17A8.70401@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
			   struct futex_hash_bucket *hb)
{
	get_futex_key_refs(key);
	q->key = *key;

	WARN_ON(plist_node_empty(&q->list));
	plist_del(&q->list, &q->list.plist);

	WARN_ON(!q->rt_waiter);
	q->rt_waiter = NULL;

	q->lock_ptr = &hb->lock;
#ifdef CONFIG_DEBUG_PI_LIST
	q->list.plist.spinlock = &hb->lock;
#endif

	wake_up_state(q->task, TASK_NORMAL);
}

void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
			   struct futex_hash_bucket *hb)
{
	get_futex_key_refs(key);
	q->key = *key;

	WARN_ON(plist_node_empty(&q->list));
	plist_del(&q->list, &q->list.plist);

	WARN_ON(!q->rt_waiter);
	q->rt_waiter = NULL;

	q->lock_ptr = &hb->lock;
#ifdef CONFIG_DEBUG_PI_LIST
	q->list.plist.spinlock = &hb->lock;
#endif

	wake_up_state(q->task, TASK_NORMAL);
}
