path: root/litmus/rsm_lock.c

#include <linux/slab.h>
#include <linux/uaccess.h>

#include <litmus/trace.h>
#include <litmus/sched_plugin.h>
#include <litmus/rsm_lock.h>

//#include <litmus/edf_common.h>

#if defined(CONFIG_LITMUS_AFFINITY_LOCKING) && defined(CONFIG_LITMUS_NVIDIA)
#include <litmus/gpu_affinity.h>
#endif


/* caller is responsible for locking */
static struct task_struct* rsm_mutex_find_hp_waiter(struct rsm_mutex *mutex,
                                             struct task_struct* skip)
{
    wait_queue_t        *q;
    struct list_head    *pos;
    struct task_struct  *queued = NULL, *found = NULL;

#ifdef CONFIG_LITMUS_DGL_SUPPORT
    dgl_wait_state_t    *dgl_wait = NULL;
#endif

    list_for_each(pos, &mutex->wait.task_list) {
        q = list_entry(pos, wait_queue_t, task_list);

#ifdef CONFIG_LITMUS_DGL_SUPPORT
        if(q->func == dgl_wake_up) {
            dgl_wait = (dgl_wait_state_t*) q->private;
            if(tsk_rt(dgl_wait->task)->blocked_lock == &mutex->litmus_lock) {
                queued = dgl_wait->task;
            }
            else {
                queued = NULL;  // skip it.
            }
        }
        else {
            queued = (struct task_struct*) q->private;
        }
#else
        queued = (struct task_struct*) q->private;
#endif

        /* Compare task prios, find high prio task. */
        //if (queued && queued != skip && edf_higher_prio(queued, found)) {
		if (queued && queued != skip && litmus->compare(queued, found)) {
            found = queued;
        }
    }
    return found;
}


#ifdef CONFIG_LITMUS_DGL_SUPPORT

int rsm_mutex_is_owner(struct litmus_lock *l, struct task_struct *t)
{
	struct rsm_mutex *mutex = rsm_mutex_from_lock(l);
	return(mutex->owner == t);
}

// return 1 if resource was immediatly acquired.
// Assumes mutex->lock is held.
// Must set task state to TASK_UNINTERRUPTIBLE if task blocks.
int rsm_mutex_dgl_lock(struct litmus_lock *l, dgl_wait_state_t* dgl_wait,
					   wait_queue_t* wq_node)
{
	struct rsm_mutex *mutex = rsm_mutex_from_lock(l);
	struct task_struct *t = dgl_wait->task;

	int acquired_immediatly = 0;

	BUG_ON(t != current);

	if (mutex->owner) {
		TRACE_TASK(t, "Enqueuing on lock %d.\n", l->ident);

		init_dgl_waitqueue_entry(wq_node, dgl_wait);

		set_task_state(t, TASK_UNINTERRUPTIBLE);
		__add_wait_queue_tail_exclusive(&mutex->wait, wq_node);
	} else {
		TRACE_TASK(t, "Acquired lock %d with no blocking.\n", l->ident);

		/* it's ours now */
		mutex->owner = t;

		raw_spin_lock(&tsk_rt(t)->hp_blocked_tasks_lock);
		binheap_add(&l->nest.hp_binheap_node, &tsk_rt(t)->hp_blocked_tasks,
					struct nested_info, hp_binheap_node);
		raw_spin_unlock(&tsk_rt(t)->hp_blocked_tasks_lock);

		acquired_immediatly = 1;
	}

	return acquired_immediatly;
}

void rsm_mutex_enable_priority(struct litmus_lock *l,
							   dgl_wait_state_t* dgl_wait)
{
	struct rsm_mutex *mutex = rsm_mutex_from_lock(l);
	struct task_struct *t = dgl_wait->task;
	struct task_struct *owner = mutex->owner;
	unsigned long flags = 0;  // these are unused under DGL coarse-grain locking

	BUG_ON(owner == t);

	tsk_rt(t)->blocked_lock = l;
	mb();

	//if (edf_higher_prio(t, mutex->hp_waiter)) {
	if (litmus->compare(t, mutex->hp_waiter)) {

		struct task_struct *old_max_eff_prio;
		struct task_struct *new_max_eff_prio;
		struct task_struct *new_prio = NULL;

		if(mutex->hp_waiter)
			TRACE_TASK(t, "has higher prio than hp_waiter (%s/%d).\n",
					   mutex->hp_waiter->comm, mutex->hp_waiter->pid);
		else
			TRACE_TASK(t, "has higher prio than hp_waiter (NIL).\n");

		raw_spin_lock(&tsk_rt(owner)->hp_blocked_tasks_lock);

		old_max_eff_prio = top_priority(&tsk_rt(owner)->hp_blocked_tasks);
		mutex->hp_waiter = t;
		l->nest.hp_waiter_eff_prio = effective_priority(mutex->hp_waiter);
		binheap_decrease(&l->nest.hp_binheap_node,
						 &tsk_rt(owner)->hp_blocked_tasks);
		new_max_eff_prio = top_priority(&tsk_rt(owner)->hp_blocked_tasks);

		if(new_max_eff_prio != old_max_eff_prio) {
			TRACE_TASK(t, "is new hp_waiter.\n");

			if ((effective_priority(owner) == old_max_eff_prio) ||
				//(__edf_higher_prio(new_max_eff_prio, BASE, owner, EFFECTIVE))){
				(litmus->__compare(new_max_eff_prio, BASE, owner, EFFECTIVE))){
				new_prio = new_max_eff_prio;
			}
		}
		else {
			TRACE_TASK(t, "no change in max_eff_prio of heap.\n");
		}

		if(new_prio) {
			litmus->nested_increase_prio(owner, new_prio,
										 &mutex->lock, flags);  // unlocks lock.
		}
		else {
			raw_spin_unlock(&tsk_rt(owner)->hp_blocked_tasks_lock);
			unlock_fine_irqrestore(&mutex->lock, flags);
		}
	}
	else {
		TRACE_TASK(t, "no change in hp_waiter.\n");
		unlock_fine_irqrestore(&mutex->lock, flags);
	}
}

static void select_next_lock_if_primary(struct litmus_lock *l,
										dgl_wait_state_t *dgl_wait)
{
	if(tsk_rt(dgl_wait->task)->blocked_lock == l) {
		TRACE_CUR("Lock %d in DGL was primary for %s/%d.\n",
				  l->ident, dgl_wait->task->comm, dgl_wait->task->pid);
		tsk_rt(dgl_wait->task)->blocked_lock = NULL;
		mb();
		select_next_lock(dgl_wait /*, l*/);  // pick the next lock to be blocked on
	}
	else {
		TRACE_CUR("Got lock early! Lock %d in DGL was NOT primary for %s/%d.\n",
				  l->ident, dgl_wait->task->comm, dgl_wait->task->pid);
	}
}
#endif




int rsm_mutex_lock(struct litmus_lock* l)
{
	struct task_struct *t = current;
	struct task_struct *owner;
	struct rsm_mutex *mutex = rsm_mutex_from_lock(l);
	wait_queue_t wait;
	unsigned long flags;

#ifdef CONFIG_LITMUS_DGL_SUPPORT
	raw_spinlock_t *dgl_lock;
#endif

	if (!is_realtime(t))
		return -EPERM;

#ifdef CONFIG_LITMUS_DGL_SUPPORT
	dgl_lock = litmus->get_dgl_spinlock(t);
#endif

	lock_global_irqsave(dgl_lock, flags);
	lock_fine_irqsave(&mutex->lock, flags);

	if (mutex->owner) {
		TRACE_TASK(t, "Blocking on lock %d.\n", l->ident);

#if defined(CONFIG_LITMUS_AFFINITY_LOCKING) && defined(CONFIG_LITMUS_NVIDIA)
		// KLUDGE: don't count this suspension as time in the critical gpu
		// critical section
		if(tsk_rt(t)->held_gpus) {
			tsk_rt(t)->suspend_gpu_tracker_on_block = 1;
		}
#endif

		/* resource is not free => must suspend and wait */

		owner = mutex->owner;

		init_waitqueue_entry(&wait, t);

		tsk_rt(t)->blocked_lock = l;  /* record where we are blocked */
		mb();  // needed?

		/* FIXME: interruptible would be nice some day */
		set_task_state(t, TASK_UNINTERRUPTIBLE);

		__add_wait_queue_tail_exclusive(&mutex->wait, &wait);

		/* check if we need to activate priority inheritance */
		//if (edf_higher_prio(t, mutex->hp_waiter)) {
		if (litmus->compare(t, mutex->hp_waiter)) {

			struct task_struct *old_max_eff_prio;
			struct task_struct *new_max_eff_prio;
			struct task_struct *new_prio = NULL;

			if(mutex->hp_waiter)
				TRACE_TASK(t, "has higher prio than hp_waiter (%s/%d).\n",
						   mutex->hp_waiter->comm, mutex->hp_waiter->pid);
			else
				TRACE_TASK(t, "has higher prio than hp_waiter (NIL).\n");

			raw_spin_lock(&tsk_rt(owner)->hp_blocked_tasks_lock);

			old_max_eff_prio = top_priority(&tsk_rt(owner)->hp_blocked_tasks);
			mutex->hp_waiter = t;
			l->nest.hp_waiter_eff_prio = effective_priority(mutex->hp_waiter);
			binheap_decrease(&l->nest.hp_binheap_node,
							 &tsk_rt(owner)->hp_blocked_tasks);
			new_max_eff_prio = top_priority(&tsk_rt(owner)->hp_blocked_tasks);

			if(new_max_eff_prio != old_max_eff_prio) {
				TRACE_TASK(t, "is new hp_waiter.\n");

				if ((effective_priority(owner) == old_max_eff_prio) ||
					//(__edf_higher_prio(new_max_eff_prio, BASE, owner, EFFECTIVE))){
					(litmus->__compare(new_max_eff_prio, BASE, owner, EFFECTIVE))){
					new_prio = new_max_eff_prio;
				}
			}
			else {
				TRACE_TASK(t, "no change in max_eff_prio of heap.\n");
			}

			if(new_prio) {
				litmus->nested_increase_prio(owner, new_prio, &mutex->lock,
											 flags);  // unlocks lock.
			}
			else {
				raw_spin_unlock(&tsk_rt(owner)->hp_blocked_tasks_lock);
				unlock_fine_irqrestore(&mutex->lock, flags);
			}
		}
		else {
			TRACE_TASK(t, "no change in hp_waiter.\n");

			unlock_fine_irqrestore(&mutex->lock, flags);
		}

		unlock_global_irqrestore(dgl_lock, flags);

		TS_LOCK_SUSPEND;

		/* We depend on the FIFO order.  Thus, we don't need to recheck
		 * when we wake up; we are guaranteed to have the lock since
		 * there is only one wake up per release.
		 */

		schedule();

		TS_LOCK_RESUME;

		/* Since we hold the lock, no other task will change
		 * ->owner. We can thus check it without acquiring the spin
		 * lock. */
		BUG_ON(mutex->owner != t);

		TRACE_TASK(t, "Acquired lock %d.\n", l->ident);

	} else {
		TRACE_TASK(t, "Acquired lock %d with no blocking.\n", l->ident);

		/* it's ours now */
		mutex->owner = t;

		raw_spin_lock(&tsk_rt(mutex->owner)->hp_blocked_tasks_lock);
		binheap_add(&l->nest.hp_binheap_node, &tsk_rt(t)->hp_blocked_tasks,
					struct nested_info, hp_binheap_node);
		raw_spin_unlock(&tsk_rt(mutex->owner)->hp_blocked_tasks_lock);


		unlock_fine_irqrestore(&mutex->lock, flags);
		unlock_global_irqrestore(dgl_lock, flags);
	}

	return 0;
}



int rsm_mutex_unlock(struct litmus_lock* l)
{
	struct task_struct *t = current, *next = NULL;
	struct rsm_mutex *mutex = rsm_mutex_from_lock(l);
	unsigned long flags;

	struct task_struct *old_max_eff_prio;

	int wake_up_task = 1;

#ifdef CONFIG_LITMUS_DGL_SUPPORT
	dgl_wait_state_t *dgl_wait = NULL;
	raw_spinlock_t *dgl_lock = litmus->get_dgl_spinlock(t);
#endif

	int err = 0;

	if (mutex->owner != t) {
		err = -EINVAL;
		return err;
	}

	lock_global_irqsave(dgl_lock, flags);
	lock_fine_irqsave(&mutex->lock, flags);

	raw_spin_lock(&tsk_rt(t)->hp_blocked_tasks_lock);

	TRACE_TASK(t, "Freeing lock %d\n", l->ident);

	old_max_eff_prio = top_priority(&tsk_rt(t)->hp_blocked_tasks);
	binheap_delete(&l->nest.hp_binheap_node, &tsk_rt(t)->hp_blocked_tasks);

	if(tsk_rt(t)->inh_task){
		struct task_struct *new_max_eff_prio =
			top_priority(&tsk_rt(t)->hp_blocked_tasks);

		if((new_max_eff_prio == NULL) ||
		      /* there was a change in eff prio */
		   (  (new_max_eff_prio != old_max_eff_prio) &&
			/* and owner had the old eff prio */
			  (effective_priority(t) == old_max_eff_prio))  )
		{
			// old_max_eff_prio > new_max_eff_prio

			//if(__edf_higher_prio(new_max_eff_prio, BASE, t, EFFECTIVE)) {
			if(litmus->__compare(new_max_eff_prio, BASE, t, EFFECTIVE)) {
				TRACE_TASK(t, "new_max_eff_prio > task's eff_prio-- new_max_eff_prio: %s/%d   task: %s/%d [%s/%d]\n",
						   new_max_eff_prio->comm, new_max_eff_prio->pid,
						   t->comm, t->pid, tsk_rt(t)->inh_task->comm,
						   tsk_rt(t)->inh_task->pid);
				WARN_ON(1);
			}

			litmus->decrease_prio(t, new_max_eff_prio);
		}
	}

	if(binheap_empty(&tsk_rt(t)->hp_blocked_tasks) &&
	   tsk_rt(t)->inh_task != NULL)
	{
		WARN_ON(tsk_rt(t)->inh_task != NULL);
		TRACE_TASK(t, "No more locks are held, but eff_prio = %s/%d\n",
				   tsk_rt(t)->inh_task->comm, tsk_rt(t)->inh_task->pid);
	}

	raw_spin_unlock(&tsk_rt(t)->hp_blocked_tasks_lock);


	/* check if there are jobs waiting for this resource */
#ifdef CONFIG_LITMUS_DGL_SUPPORT
	__waitqueue_dgl_remove_first(&mutex->wait, &dgl_wait, &next);
	if(dgl_wait) {
		next = dgl_wait->task;
		//select_next_lock_if_primary(l, dgl_wait);
	}
#else
	next = __waitqueue_remove_first(&mutex->wait);
#endif
	if (next) {
		/* next becomes the resouce holder */
		mutex->owner = next;
		TRACE_CUR("lock ownership passed to %s/%d\n", next->comm, next->pid);

		/* determine new hp_waiter if necessary */
		if (next == mutex->hp_waiter) {

			TRACE_TASK(next, "was highest-prio waiter\n");
			/* next has the highest priority --- it doesn't need to
			 * inherit.  However, we need to make sure that the
			 * next-highest priority in the queue is reflected in
			 * hp_waiter. */
			mutex->hp_waiter = rsm_mutex_find_hp_waiter(mutex, next);
			l->nest.hp_waiter_eff_prio = (mutex->hp_waiter) ?
				effective_priority(mutex->hp_waiter) :
				NULL;

			if (mutex->hp_waiter)
				TRACE_TASK(mutex->hp_waiter, "is new highest-prio waiter\n");
			else
				TRACE("no further waiters\n");

			raw_spin_lock(&tsk_rt(next)->hp_blocked_tasks_lock);

			binheap_add(&l->nest.hp_binheap_node,
						&tsk_rt(next)->hp_blocked_tasks,
						struct nested_info, hp_binheap_node);

#ifdef CONFIG_LITMUS_DGL_SUPPORT
			if(dgl_wait) {
				select_next_lock_if_primary(l, dgl_wait);
				//wake_up_task = atomic_dec_and_test(&dgl_wait->nr_remaining);
				--(dgl_wait->nr_remaining);
				wake_up_task = (dgl_wait->nr_remaining == 0);
			}
#endif
			raw_spin_unlock(&tsk_rt(next)->hp_blocked_tasks_lock);
		}
		else {
			/* Well, if 'next' is not the highest-priority waiter,
			 * then it (probably) ought to inherit the highest-priority
			 * waiter's priority. */
			TRACE_TASK(next, "is not hp_waiter of lock %d.\n", l->ident);

			raw_spin_lock(&tsk_rt(next)->hp_blocked_tasks_lock);

			binheap_add(&l->nest.hp_binheap_node,
						&tsk_rt(next)->hp_blocked_tasks,
						struct nested_info, hp_binheap_node);

#ifdef CONFIG_LITMUS_DGL_SUPPORT
			if(dgl_wait) {
				select_next_lock_if_primary(l, dgl_wait);
				--(dgl_wait->nr_remaining);
				wake_up_task = (dgl_wait->nr_remaining == 0);
			}
#endif

			/* It is possible that 'next' *should* be the hp_waiter, but isn't
		     * because that update hasn't yet executed (update operation is
			 * probably blocked on mutex->lock). So only inherit if the top of
			 * 'next's top heap node is indeed the effective prio. of hp_waiter.
			 * (We use l->hp_waiter_eff_prio instead of effective_priority(hp_waiter)
			 * since the effective priority of hp_waiter can change (and the
			 * update has not made it to this lock).)
			 */
#ifdef CONFIG_LITMUS_DGL_SUPPORT
			if((l->nest.hp_waiter_eff_prio != NULL) &&
			   (top_priority(&tsk_rt(next)->hp_blocked_tasks) ==
													l->nest.hp_waiter_eff_prio))
			{
				if(dgl_wait && tsk_rt(next)->blocked_lock) {
					BUG_ON(wake_up_task);
					//if(__edf_higher_prio(l->nest.hp_waiter_eff_prio, BASE, next, EFFECTIVE)) {
					if(litmus->__compare(l->nest.hp_waiter_eff_prio, BASE, next, EFFECTIVE)) {
						litmus->nested_increase_prio(next,
							l->nest.hp_waiter_eff_prio, &mutex->lock, flags);  // unlocks lock && hp_blocked_tasks_lock.
						goto out;  // all spinlocks are released.  bail out now.
					}
				}
				else {
					litmus->increase_prio(next, l->nest.hp_waiter_eff_prio);
				}
			}

			raw_spin_unlock(&tsk_rt(next)->hp_blocked_tasks_lock);
#else
			if(likely(top_priority(&tsk_rt(next)->hp_blocked_tasks) ==
													l->nest.hp_waiter_eff_prio))
			{
				litmus->increase_prio(next, l->nest.hp_waiter_eff_prio);
			}
			raw_spin_unlock(&tsk_rt(next)->hp_blocked_tasks_lock);
#endif
		}

		if(wake_up_task) {
			TRACE_TASK(next, "waking up since it is no longer blocked.\n");

			tsk_rt(next)->blocked_lock = NULL;
			mb();

#if defined(CONFIG_LITMUS_AFFINITY_LOCKING) && defined(CONFIG_LITMUS_NVIDIA)
			// re-enable tracking
			if(tsk_rt(next)->held_gpus) {
				tsk_rt(next)->suspend_gpu_tracker_on_block = 0;
			}
#endif

			wake_up_process(next);
		}
		else {
			TRACE_TASK(next, "is still blocked.\n");
		}
	}
	else {
		/* becomes available */
		mutex->owner = NULL;
	}

	unlock_fine_irqrestore(&mutex->lock, flags);

#ifdef CONFIG_LITMUS_DGL_SUPPORT
out:
#endif
	unlock_global_irqrestore(dgl_lock, flags);

	return err;
}


void rsm_mutex_propagate_increase_inheritance(struct litmus_lock* l,
											struct task_struct* t,
											raw_spinlock_t* to_unlock,
											unsigned long irqflags)
{
	struct rsm_mutex *mutex = rsm_mutex_from_lock(l);

	// relay-style locking
	lock_fine(&mutex->lock);
	unlock_fine(to_unlock);

	if(tsk_rt(t)->blocked_lock == l) {  // prevent race on tsk_rt(t)->blocked
		struct task_struct *owner = mutex->owner;

		struct task_struct *old_max_eff_prio;
		struct task_struct *new_max_eff_prio;

		raw_spin_lock(&tsk_rt(owner)->hp_blocked_tasks_lock);

		old_max_eff_prio = top_priority(&tsk_rt(owner)->hp_blocked_tasks);

		//if((t != mutex->hp_waiter) && edf_higher_prio(t, mutex->hp_waiter)) {
		if((t != mutex->hp_waiter) && litmus->compare(t, mutex->hp_waiter)) {
			TRACE_TASK(t, "is new highest-prio waiter by propagation.\n");
			mutex->hp_waiter = t;
		}
		if(t == mutex->hp_waiter) {
			// reflect the decreased priority in the heap node.
			l->nest.hp_waiter_eff_prio = effective_priority(mutex->hp_waiter);

			BUG_ON(!binheap_is_in_heap(&l->nest.hp_binheap_node));
			BUG_ON(!binheap_is_in_this_heap(&l->nest.hp_binheap_node,
											&tsk_rt(owner)->hp_blocked_tasks));

			binheap_decrease(&l->nest.hp_binheap_node,
							 &tsk_rt(owner)->hp_blocked_tasks);
		}

		new_max_eff_prio = top_priority(&tsk_rt(owner)->hp_blocked_tasks);


		if(new_max_eff_prio != old_max_eff_prio) {
			// new_max_eff_prio > old_max_eff_prio holds.
			if ((effective_priority(owner) == old_max_eff_prio) ||
				//(__edf_higher_prio(new_max_eff_prio, BASE, owner, EFFECTIVE))) {
				(litmus->__compare(new_max_eff_prio, BASE, owner, EFFECTIVE))) {
				TRACE_CUR("Propagating inheritance to holder of lock %d.\n",
						  l->ident);

				// beware: recursion
				litmus->nested_increase_prio(owner, new_max_eff_prio,
											 &mutex->lock, irqflags);  // unlocks mutex->lock
			}
			else {
				TRACE_CUR("Lower priority than holder %s/%d.  No propagation.\n",
						  owner->comm, owner->pid);
				raw_spin_unlock(&tsk_rt(owner)->hp_blocked_tasks_lock);
				unlock_fine_irqrestore(&mutex->lock, irqflags);
			}
		}
		else {
			TRACE_TASK(mutex->owner, "No change in maxiumum effective priority.\n");
			raw_spin_unlock(&tsk_rt(owner)->hp_blocked_tasks_lock);
			unlock_fine_irqrestore(&mutex->lock, irqflags);
		}
	}
	else {
		struct litmus_lock *still_blocked = tsk_rt(t)->blocked_lock;

		TRACE_TASK(t, "is not blocked on lock %d.\n", l->ident);
		if(still_blocked) {
			TRACE_TASK(t, "is still blocked on a lock though (lock %d).\n",
					   still_blocked->ident);
			if(still_blocked->ops->propagate_increase_inheritance) {
				/* due to relay-style nesting of spinlocks (acq. A, acq. B, free A, free B)
				 we know that task 't' has not released any locks behind us in this
				 chain.  Propagation just needs to catch up with task 't'. */
				still_blocked->ops->propagate_increase_inheritance(still_blocked,
																   t,
																   &mutex->lock,
																   irqflags);
			}
			else {
				TRACE_TASK(t,
						   "Inheritor is blocked on lock (%p) that does not "
						   "support nesting!\n",
						   still_blocked);
				unlock_fine_irqrestore(&mutex->lock, irqflags);
			}
		}
		else {
			unlock_fine_irqrestore(&mutex->lock, irqflags);
		}
	}
}


void rsm_mutex_propagate_decrease_inheritance(struct litmus_lock* l,
											 struct task_struct* t,
											 raw_spinlock_t* to_unlock,
											 unsigned long irqflags)
{
	struct rsm_mutex *mutex = rsm_mutex_from_lock(l);

	// relay-style locking
	lock_fine(&mutex->lock);
	unlock_fine(to_unlock);

	if(tsk_rt(t)->blocked_lock == l) {  // prevent race on tsk_rt(t)->blocked
		if(t == mutex->hp_waiter) {
			struct task_struct *owner = mutex->owner;

			struct task_struct *old_max_eff_prio;
			struct task_struct *new_max_eff_prio;

			raw_spin_lock(&tsk_rt(owner)->hp_blocked_tasks_lock);

			old_max_eff_prio = top_priority(&tsk_rt(owner)->hp_blocked_tasks);

			binheap_delete(&l->nest.hp_binheap_node, &tsk_rt(owner)->hp_blocked_tasks);
			mutex->hp_waiter = rsm_mutex_find_hp_waiter(mutex, NULL);
			l->nest.hp_waiter_eff_prio = (mutex->hp_waiter) ?
				effective_priority(mutex->hp_waiter) : NULL;
			binheap_add(&l->nest.hp_binheap_node,
						&tsk_rt(owner)->hp_blocked_tasks,
						struct nested_info, hp_binheap_node);

			new_max_eff_prio = top_priority(&tsk_rt(owner)->hp_blocked_tasks);

			if((old_max_eff_prio != new_max_eff_prio) &&
			   (effective_priority(owner) == old_max_eff_prio))
			{
				// Need to set new effective_priority for owner

				struct task_struct *decreased_prio;

				TRACE_CUR("Propagating decreased inheritance to holder of lock %d.\n",
						  l->ident);

				//if(__edf_higher_prio(new_max_eff_prio, BASE, owner, BASE)) {
				if(litmus->__compare(new_max_eff_prio, BASE, owner, BASE)) {
					TRACE_CUR("%s/%d has greater base priority than base priority of owner (%s/%d) of lock %d.\n",
							  (new_max_eff_prio) ? new_max_eff_prio->comm : "nil",
							  (new_max_eff_prio) ? new_max_eff_prio->pid : -1,
							  owner->comm,
							  owner->pid,
							  l->ident);

					decreased_prio = new_max_eff_prio;
				}
				else {
					TRACE_CUR("%s/%d has lesser base priority than base priority of owner (%s/%d) of lock %d.\n",
							  (new_max_eff_prio) ? new_max_eff_prio->comm : "nil",
							  (new_max_eff_prio) ? new_max_eff_prio->pid : -1,
							  owner->comm,
							  owner->pid,
							  l->ident);

					decreased_prio = NULL;
				}

				// beware: recursion
				litmus->nested_decrease_prio(owner, decreased_prio, &mutex->lock, irqflags);	// will unlock mutex->lock
			}
			else {
				raw_spin_unlock(&tsk_rt(owner)->hp_blocked_tasks_lock);
				unlock_fine_irqrestore(&mutex->lock, irqflags);
			}
		}
		else {
			TRACE_TASK(t, "is not hp_waiter.  No propagation.\n");
			unlock_fine_irqrestore(&mutex->lock, irqflags);
		}
	}
	else {
		struct litmus_lock *still_blocked = tsk_rt(t)->blocked_lock;

		TRACE_TASK(t, "is not blocked on lock %d.\n", l->ident);
		if(still_blocked) {
			TRACE_TASK(t, "is still blocked on a lock though (lock %d).\n",
					   still_blocked->ident);
			if(still_blocked->ops->propagate_decrease_inheritance) {
				/* due to linked nesting of spinlocks (acq. A, acq. B, free A, free B)
				 we know that task 't' has not released any locks behind us in this
				 chain.  propagation just needs to catch up with task 't' */
				still_blocked->ops->propagate_decrease_inheritance(still_blocked,
																   t,
																   &mutex->lock,
																   irqflags);
			}
			else {
				TRACE_TASK(t, "Inheritor is blocked on lock (%p) that does not support nesting!\n",
						   still_blocked);
				unlock_fine_irqrestore(&mutex->lock, irqflags);
			}
		}
		else {
			unlock_fine_irqrestore(&mutex->lock, irqflags);
		}
	}
}


int rsm_mutex_close(struct litmus_lock* l)
{
	struct task_struct *t = current;
	struct rsm_mutex *mutex = rsm_mutex_from_lock(l);
	unsigned long flags;

	int owner;

#ifdef CONFIG_LITMUS_DGL_SUPPORT
	raw_spinlock_t *dgl_lock = litmus->get_dgl_spinlock(t);
#endif

	lock_global_irqsave(dgl_lock, flags);
	lock_fine_irqsave(&mutex->lock, flags);

	owner = (mutex->owner == t);

	unlock_fine_irqrestore(&mutex->lock, flags);
	unlock_global_irqrestore(dgl_lock, flags);

	if (owner)
		rsm_mutex_unlock(l);

	return 0;
}

void rsm_mutex_free(struct litmus_lock* lock)
{
	kfree(rsm_mutex_from_lock(lock));
}

struct litmus_lock* rsm_mutex_new(struct litmus_lock_ops* ops)
{
	struct rsm_mutex* mutex;

	mutex = kmalloc(sizeof(*mutex), GFP_KERNEL);
	if (!mutex)
		return NULL;

	mutex->litmus_lock.ops = ops;
	mutex->owner   = NULL;
	mutex->hp_waiter = NULL;
	init_waitqueue_head(&mutex->wait);


#ifdef CONFIG_DEBUG_SPINLOCK
	{
		__raw_spin_lock_init(&mutex->lock,
							 ((struct litmus_lock*)mutex)->cheat_lockdep,
							 &((struct litmus_lock*)mutex)->key);
	}
#else
	raw_spin_lock_init(&mutex->lock);
#endif

	((struct litmus_lock*)mutex)->nest.hp_waiter_ptr = &mutex->hp_waiter;

	return &mutex->litmus_lock;
}