/*
   * RT-Mutexes: simple blocking mutual exclusion locks with PI support
   *
   * started by Ingo Molnar and Thomas Gleixner.
   *
   *  Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   *  Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
   *  Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
   *  Copyright (C) 2006 Esben Nielsen

   *
   *  See Documentation/rt-mutex-design.txt for details.

   */
  #include <linux/spinlock.h>
  #include <linux/module.h>
  #include <linux/sched.h>
  #include <linux/timer.h>
  
  #include "rtmutex_common.h"

  /*
   * lock->owner state tracking:
   *
   * lock->owner holds the task_struct pointer of the owner. Bit 0 and 1
   * are used to keep track of the "owner is pending" and "lock has
   * waiters" state.
   *
   * owner	bit1	bit0
   * NULL		0	0	lock is free (fast acquire possible)
   * NULL		0	1	invalid state
   * NULL		1	0	Transitional State*
   * NULL		1	1	invalid state
   * taskpointer	0	0	lock is held (fast release possible)
   * taskpointer	0	1	task is pending owner
   * taskpointer	1	0	lock is held and has waiters
   * taskpointer	1	1	task is pending owner and lock has more waiters
   *
   * Pending ownership is assigned to the top (highest priority)
   * waiter of the lock, when the lock is released. The thread is woken
   * up and can now take the lock. Until the lock is taken (bit 0
   * cleared) a competing higher priority thread can steal the lock
   * which puts the woken up thread back on the waiters list.
   *
   * The fast atomic compare exchange based acquire and release is only
   * possible when bit 0 and 1 of lock->owner are 0.
   *
   * (*) There's a small time where the owner can be NULL and the
   * "lock has waiters" bit is set.  This can happen when grabbing the lock.
   * To prevent a cmpxchg of the owner releasing the lock, we need to set this
   * bit before looking at the lock, hence the reason this is a transitional
   * state.
   */

  static void

  rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner,
  		   unsigned long mask)
  {
  	unsigned long val = (unsigned long)owner | mask;
  
  	if (rt_mutex_has_waiters(lock))
  		val |= RT_MUTEX_HAS_WAITERS;
  
  	lock->owner = (struct task_struct *)val;
  }
  
  static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
  {
  	lock->owner = (struct task_struct *)
  			((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
  }
  
  static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  {
  	if (!rt_mutex_has_waiters(lock))
  		clear_rt_mutex_waiters(lock);
  }
  
  /*

   * We can speed up the acquire/release, if the architecture
   * supports cmpxchg and if there's no debugging state to be set up
   */
  #if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
  # define rt_mutex_cmpxchg(l,c,n)	(cmpxchg(&l->owner, c, n) == c)
  static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  {
  	unsigned long owner, *p = (unsigned long *) &lock->owner;
  
  	do {
  		owner = *p;
  	} while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
  }
  #else
  # define rt_mutex_cmpxchg(l,c,n)	(0)
  static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  {
  	lock->owner = (struct task_struct *)
  			((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
  }
  #endif
  
  /*

   * Calculate task priority from the waiter list priority
   *
   * Return task->normal_prio when the waiter list is empty or when
   * the waiter is not allowed to do priority boosting
   */
  int rt_mutex_getprio(struct task_struct *task)
  {
  	if (likely(!task_has_pi_waiters(task)))
  		return task->normal_prio;
  
  	return min(task_top_pi_waiter(task)->pi_list_entry.prio,
  		   task->normal_prio);
  }
  
  /*
   * Adjust the priority of a task, after its pi_waiters got modified.
   *
   * This can be both boosting and unboosting. task->pi_lock must be held.
   */

  static void __rt_mutex_adjust_prio(struct task_struct *task)

  {
  	int prio = rt_mutex_getprio(task);
  
  	if (task->prio != prio)
  		rt_mutex_setprio(task, prio);
  }
  
  /*
   * Adjust task priority (undo boosting). Called from the exit path of
   * rt_mutex_slowunlock() and rt_mutex_slowlock().
   *
   * (Note: We do this outside of the protection of lock->wait_lock to
   * allow the lock to be taken while or before we readjust the priority
   * of task. We do not use the spin_xx_mutex() variants here as we are
   * outside of the debug path.)
   */
  static void rt_mutex_adjust_prio(struct task_struct *task)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&task->pi_lock, flags);
  	__rt_mutex_adjust_prio(task);
  	spin_unlock_irqrestore(&task->pi_lock, flags);
  }
  
  /*
   * Max number of times we'll walk the boosting chain:
   */
  int max_lock_depth = 1024;
  
  /*
   * Adjust the priority chain. Also used for deadlock detection.
   * Decreases task's usage by one - may thus free the task.
   * Returns 0 or -EDEADLK.
   */

  static int rt_mutex_adjust_prio_chain(struct task_struct *task,
  				      int deadlock_detect,
  				      struct rt_mutex *orig_lock,
  				      struct rt_mutex_waiter *orig_waiter,
  				      struct task_struct *top_task)

  {
  	struct rt_mutex *lock;
  	struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
  	int detect_deadlock, ret = 0, depth = 0;
  	unsigned long flags;
  
  	detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
  							 deadlock_detect);
  
  	/*
  	 * The (de)boosting is a step by step approach with a lot of
  	 * pitfalls. We want this to be preemptible and we want hold a
  	 * maximum of two locks per step. So we have to check
  	 * carefully whether things change under us.
  	 */
   again:
  	if (++depth > max_lock_depth) {
  		static int prev_max;
  
  		/*
  		 * Print this only once. If the admin changes the limit,
  		 * print a new message when reaching the limit again.
  		 */
  		if (prev_max != max_lock_depth) {
  			prev_max = max_lock_depth;
  			printk(KERN_WARNING "Maximum lock depth %d reached "
  			       "task: %s (%d)
  ", max_lock_depth,

  			       top_task->comm, task_pid_nr(top_task));

  		}
  		put_task_struct(task);
  
  		return deadlock_detect ? -EDEADLK : 0;
  	}
   retry:
  	/*
  	 * Task can not go away as we did a get_task() before !
  	 */
  	spin_lock_irqsave(&task->pi_lock, flags);
  
  	waiter = task->pi_blocked_on;
  	/*
  	 * Check whether the end of the boosting chain has been
  	 * reached or the state of the chain has changed while we
  	 * dropped the locks.
  	 */
  	if (!waiter || !waiter->task)
  		goto out_unlock_pi;

  	/*
  	 * Check the orig_waiter state. After we dropped the locks,
  	 * the previous owner of the lock might have released the lock
  	 * and made us the pending owner:
  	 */
  	if (orig_waiter && !orig_waiter->task)
  		goto out_unlock_pi;
  
  	/*
  	 * Drop out, when the task has no waiters. Note,
  	 * top_waiter can be NULL, when we are in the deboosting
  	 * mode!
  	 */

  	if (top_waiter && (!task_has_pi_waiters(task) ||
  			   top_waiter != task_top_pi_waiter(task)))
  		goto out_unlock_pi;
  
  	/*
  	 * When deadlock detection is off then we check, if further
  	 * priority adjustment is necessary.
  	 */
  	if (!detect_deadlock && waiter->list_entry.prio == task->prio)
  		goto out_unlock_pi;
  
  	lock = waiter->lock;
  	if (!spin_trylock(&lock->wait_lock)) {
  		spin_unlock_irqrestore(&task->pi_lock, flags);
  		cpu_relax();
  		goto retry;
  	}
  
  	/* Deadlock detection */

  	if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {

  		debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
  		spin_unlock(&lock->wait_lock);
  		ret = deadlock_detect ? -EDEADLK : 0;
  		goto out_unlock_pi;
  	}
  
  	top_waiter = rt_mutex_top_waiter(lock);
  
  	/* Requeue the waiter */
  	plist_del(&waiter->list_entry, &lock->wait_list);
  	waiter->list_entry.prio = task->prio;
  	plist_add(&waiter->list_entry, &lock->wait_list);
  
  	/* Release the task */
  	spin_unlock_irqrestore(&task->pi_lock, flags);
  	put_task_struct(task);
  
  	/* Grab the next task */
  	task = rt_mutex_owner(lock);

  	get_task_struct(task);

  	spin_lock_irqsave(&task->pi_lock, flags);
  
  	if (waiter == rt_mutex_top_waiter(lock)) {
  		/* Boost the owner */
  		plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
  		waiter->pi_list_entry.prio = waiter->list_entry.prio;
  		plist_add(&waiter->pi_list_entry, &task->pi_waiters);
  		__rt_mutex_adjust_prio(task);
  
  	} else if (top_waiter == waiter) {
  		/* Deboost the owner */
  		plist_del(&waiter->pi_list_entry, &task->pi_waiters);
  		waiter = rt_mutex_top_waiter(lock);
  		waiter->pi_list_entry.prio = waiter->list_entry.prio;
  		plist_add(&waiter->pi_list_entry, &task->pi_waiters);
  		__rt_mutex_adjust_prio(task);
  	}

  	spin_unlock_irqrestore(&task->pi_lock, flags);
  
  	top_waiter = rt_mutex_top_waiter(lock);
  	spin_unlock(&lock->wait_lock);
  
  	if (!detect_deadlock && waiter != top_waiter)
  		goto out_put_task;
  
  	goto again;
  
   out_unlock_pi:
  	spin_unlock_irqrestore(&task->pi_lock, flags);
   out_put_task:
  	put_task_struct(task);

  	return ret;
  }
  
  /*
   * Optimization: check if we can steal the lock from the
   * assigned pending owner [which might not have taken the
   * lock yet]:
   */
  static inline int try_to_steal_lock(struct rt_mutex *lock)
  {
  	struct task_struct *pendowner = rt_mutex_owner(lock);
  	struct rt_mutex_waiter *next;
  	unsigned long flags;
  
  	if (!rt_mutex_owner_pending(lock))
  		return 0;
  
  	if (pendowner == current)
  		return 1;
  
  	spin_lock_irqsave(&pendowner->pi_lock, flags);
  	if (current->prio >= pendowner->prio) {
  		spin_unlock_irqrestore(&pendowner->pi_lock, flags);
  		return 0;
  	}
  
  	/*
  	 * Check if a waiter is enqueued on the pending owners
  	 * pi_waiters list. Remove it and readjust pending owners
  	 * priority.
  	 */
  	if (likely(!rt_mutex_has_waiters(lock))) {
  		spin_unlock_irqrestore(&pendowner->pi_lock, flags);
  		return 1;
  	}
  
  	/* No chain handling, pending owner is not blocked on anything: */
  	next = rt_mutex_top_waiter(lock);
  	plist_del(&next->pi_list_entry, &pendowner->pi_waiters);
  	__rt_mutex_adjust_prio(pendowner);
  	spin_unlock_irqrestore(&pendowner->pi_lock, flags);
  
  	/*
  	 * We are going to steal the lock and a waiter was
  	 * enqueued on the pending owners pi_waiters queue. So
  	 * we have to enqueue this waiter into
  	 * current->pi_waiters list. This covers the case,
  	 * where current is boosted because it holds another
  	 * lock and gets unboosted because the booster is
  	 * interrupted, so we would delay a waiter with higher
  	 * priority as current->normal_prio.
  	 *
  	 * Note: in the rare case of a SCHED_OTHER task changing
  	 * its priority and thus stealing the lock, next->task
  	 * might be current:
  	 */
  	if (likely(next->task != current)) {
  		spin_lock_irqsave(&current->pi_lock, flags);
  		plist_add(&next->pi_list_entry, &current->pi_waiters);
  		__rt_mutex_adjust_prio(current);
  		spin_unlock_irqrestore(&current->pi_lock, flags);
  	}
  	return 1;
  }
  
  /*
   * Try to take an rt-mutex
   *
   * This fails
   * - when the lock has a real owner
   * - when a different pending owner exists and has higher priority than current
   *
   * Must be called with lock->wait_lock held.
   */

  static int try_to_take_rt_mutex(struct rt_mutex *lock)

  {
  	/*
  	 * We have to be careful here if the atomic speedups are
  	 * enabled, such that, when
  	 *  - no other waiter is on the lock
  	 *  - the lock has been released since we did the cmpxchg
  	 * the lock can be released or taken while we are doing the
  	 * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
  	 *
  	 * The atomic acquire/release aware variant of
  	 * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
  	 * the WAITERS bit, the atomic release / acquire can not
  	 * happen anymore and lock->wait_lock protects us from the
  	 * non-atomic case.
  	 *
  	 * Note, that this might set lock->owner =
  	 * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
  	 * any more. This is fixed up when we take the ownership.
  	 * This is the transitional state explained at the top of this file.
  	 */
  	mark_rt_mutex_waiters(lock);
  
  	if (rt_mutex_owner(lock) && !try_to_steal_lock(lock))
  		return 0;
  
  	/* We got the lock. */

  	debug_rt_mutex_lock(lock);

  
  	rt_mutex_set_owner(lock, current, 0);
  
  	rt_mutex_deadlock_account_lock(lock, current);
  
  	return 1;
  }
  
  /*
   * Task blocks on lock.
   *
   * Prepare waiter and propagate pi chain
   *
   * This must be called with lock->wait_lock held.
   */
  static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
  				   struct rt_mutex_waiter *waiter,

  				   int detect_deadlock)

  {

  	struct task_struct *owner = rt_mutex_owner(lock);

  	struct rt_mutex_waiter *top_waiter = waiter;

  	unsigned long flags;

  	int chain_walk = 0, res;

  
  	spin_lock_irqsave(&current->pi_lock, flags);
  	__rt_mutex_adjust_prio(current);
  	waiter->task = current;
  	waiter->lock = lock;
  	plist_node_init(&waiter->list_entry, current->prio);
  	plist_node_init(&waiter->pi_list_entry, current->prio);
  
  	/* Get the top priority waiter on the lock */
  	if (rt_mutex_has_waiters(lock))
  		top_waiter = rt_mutex_top_waiter(lock);
  	plist_add(&waiter->list_entry, &lock->wait_list);
  
  	current->pi_blocked_on = waiter;
  
  	spin_unlock_irqrestore(&current->pi_lock, flags);
  
  	if (waiter == rt_mutex_top_waiter(lock)) {
  		spin_lock_irqsave(&owner->pi_lock, flags);
  		plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
  		plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
  
  		__rt_mutex_adjust_prio(owner);

  		if (owner->pi_blocked_on)
  			chain_walk = 1;

  		spin_unlock_irqrestore(&owner->pi_lock, flags);
  	}

  	else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock))
  		chain_walk = 1;
  
  	if (!chain_walk)

  		return 0;

  	/*
  	 * The owner can't disappear while holding a lock,
  	 * so the owner struct is protected by wait_lock.
  	 * Gets dropped in rt_mutex_adjust_prio_chain()!
  	 */
  	get_task_struct(owner);

  	spin_unlock(&lock->wait_lock);

  	res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,

  					 current);

  
  	spin_lock(&lock->wait_lock);
  
  	return res;
  }
  
  /*
   * Wake up the next waiter on the lock.
   *
   * Remove the top waiter from the current tasks waiter list and from
   * the lock waiter list. Set it as pending owner. Then wake it up.
   *
   * Called with lock->wait_lock held.
   */
  static void wakeup_next_waiter(struct rt_mutex *lock)
  {
  	struct rt_mutex_waiter *waiter;
  	struct task_struct *pendowner;
  	unsigned long flags;
  
  	spin_lock_irqsave(&current->pi_lock, flags);
  
  	waiter = rt_mutex_top_waiter(lock);
  	plist_del(&waiter->list_entry, &lock->wait_list);
  
  	/*
  	 * Remove it from current->pi_waiters. We do not adjust a
  	 * possible priority boost right now. We execute wakeup in the
  	 * boosted mode and go back to normal after releasing
  	 * lock->wait_lock.
  	 */
  	plist_del(&waiter->pi_list_entry, &current->pi_waiters);
  	pendowner = waiter->task;
  	waiter->task = NULL;
  
  	rt_mutex_set_owner(lock, pendowner, RT_MUTEX_OWNER_PENDING);
  
  	spin_unlock_irqrestore(&current->pi_lock, flags);
  
  	/*
  	 * Clear the pi_blocked_on variable and enqueue a possible
  	 * waiter into the pi_waiters list of the pending owner. This
  	 * prevents that in case the pending owner gets unboosted a
  	 * waiter with higher priority than pending-owner->normal_prio
  	 * is blocked on the unboosted (pending) owner.
  	 */
  	spin_lock_irqsave(&pendowner->pi_lock, flags);
  
  	WARN_ON(!pendowner->pi_blocked_on);
  	WARN_ON(pendowner->pi_blocked_on != waiter);
  	WARN_ON(pendowner->pi_blocked_on->lock != lock);
  
  	pendowner->pi_blocked_on = NULL;
  
  	if (rt_mutex_has_waiters(lock)) {
  		struct rt_mutex_waiter *next;
  
  		next = rt_mutex_top_waiter(lock);
  		plist_add(&next->pi_list_entry, &pendowner->pi_waiters);
  	}
  	spin_unlock_irqrestore(&pendowner->pi_lock, flags);
  
  	wake_up_process(pendowner);
  }
  
  /*
   * Remove a waiter from a lock
   *
   * Must be called with lock->wait_lock held
   */

  static void remove_waiter(struct rt_mutex *lock,
  			  struct rt_mutex_waiter *waiter)

  {
  	int first = (waiter == rt_mutex_top_waiter(lock));

  	struct task_struct *owner = rt_mutex_owner(lock);

  	unsigned long flags;

  	int chain_walk = 0;

  
  	spin_lock_irqsave(&current->pi_lock, flags);
  	plist_del(&waiter->list_entry, &lock->wait_list);
  	waiter->task = NULL;
  	current->pi_blocked_on = NULL;
  	spin_unlock_irqrestore(&current->pi_lock, flags);
  
  	if (first && owner != current) {
  
  		spin_lock_irqsave(&owner->pi_lock, flags);
  
  		plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
  
  		if (rt_mutex_has_waiters(lock)) {
  			struct rt_mutex_waiter *next;
  
  			next = rt_mutex_top_waiter(lock);
  			plist_add(&next->pi_list_entry, &owner->pi_waiters);
  		}
  		__rt_mutex_adjust_prio(owner);

  		if (owner->pi_blocked_on)
  			chain_walk = 1;

  		spin_unlock_irqrestore(&owner->pi_lock, flags);
  	}
  
  	WARN_ON(!plist_node_empty(&waiter->pi_list_entry));

  	if (!chain_walk)

  		return;

  	/* gets dropped in rt_mutex_adjust_prio_chain()! */
  	get_task_struct(owner);

  	spin_unlock(&lock->wait_lock);

  	rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);

  
  	spin_lock(&lock->wait_lock);
  }
  
  /*

   * Recheck the pi chain, in case we got a priority setting
   *
   * Called from sched_setscheduler
   */
  void rt_mutex_adjust_pi(struct task_struct *task)
  {
  	struct rt_mutex_waiter *waiter;
  	unsigned long flags;
  
  	spin_lock_irqsave(&task->pi_lock, flags);
  
  	waiter = task->pi_blocked_on;
  	if (!waiter || waiter->list_entry.prio == task->prio) {
  		spin_unlock_irqrestore(&task->pi_lock, flags);
  		return;
  	}

  	spin_unlock_irqrestore(&task->pi_lock, flags);

  	/* gets dropped in rt_mutex_adjust_prio_chain()! */
  	get_task_struct(task);

  	rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);

  }
  
  /*

   * Slow path lock function:
   */
  static int __sched
  rt_mutex_slowlock(struct rt_mutex *lock, int state,
  		  struct hrtimer_sleeper *timeout,

  		  int detect_deadlock)

  {
  	struct rt_mutex_waiter waiter;
  	int ret = 0;
  
  	debug_rt_mutex_init_waiter(&waiter);
  	waiter.task = NULL;
  
  	spin_lock(&lock->wait_lock);
  
  	/* Try to acquire the lock again: */

  	if (try_to_take_rt_mutex(lock)) {

  		spin_unlock(&lock->wait_lock);
  		return 0;
  	}
  
  	set_current_state(state);
  
  	/* Setup the timer, when timeout != NULL */

  	if (unlikely(timeout)) {

  		hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);

  		if (!hrtimer_active(&timeout->timer))
  			timeout->task = NULL;
  	}

  
  	for (;;) {
  		/* Try to acquire the lock: */

  		if (try_to_take_rt_mutex(lock))

  			break;
  
  		/*
  		 * TASK_INTERRUPTIBLE checks for signals and
  		 * timeout. Ignored otherwise.
  		 */
  		if (unlikely(state == TASK_INTERRUPTIBLE)) {
  			/* Signal pending? */
  			if (signal_pending(current))
  				ret = -EINTR;
  			if (timeout && !timeout->task)
  				ret = -ETIMEDOUT;
  			if (ret)
  				break;
  		}
  
  		/*
  		 * waiter.task is NULL the first time we come here and
  		 * when we have been woken up by the previous owner
  		 * but the lock got stolen by a higher prio task.
  		 */
  		if (!waiter.task) {
  			ret = task_blocks_on_rt_mutex(lock, &waiter,

  						      detect_deadlock);

  			/*
  			 * If we got woken up by the owner then start loop
  			 * all over without going into schedule to try
  			 * to get the lock now:
  			 */

  			if (unlikely(!waiter.task)) {
  				/*
  				 * Reset the return value. We might
  				 * have returned with -EDEADLK and the
  				 * owner released the lock while we
  				 * were walking the pi chain.
  				 */
  				ret = 0;

  				continue;

  			}

  			if (unlikely(ret))
  				break;
  		}

  		spin_unlock(&lock->wait_lock);
  
  		debug_rt_mutex_print_deadlock(&waiter);

  		if (waiter.task)
  			schedule_rt_mutex(lock);

  
  		spin_lock(&lock->wait_lock);
  		set_current_state(state);
  	}
  
  	set_current_state(TASK_RUNNING);
  
  	if (unlikely(waiter.task))

  		remove_waiter(lock, &waiter);

  
  	/*
  	 * try_to_take_rt_mutex() sets the waiter bit
  	 * unconditionally. We might have to fix that up.
  	 */
  	fixup_rt_mutex_waiters(lock);
  
  	spin_unlock(&lock->wait_lock);
  
  	/* Remove pending timer: */
  	if (unlikely(timeout))
  		hrtimer_cancel(&timeout->timer);
  
  	/*
  	 * Readjust priority, when we did not get the lock. We might
  	 * have been the pending owner and boosted. Since we did not
  	 * take the lock, the PI boost has to go.
  	 */
  	if (unlikely(ret))
  		rt_mutex_adjust_prio(current);
  
  	debug_rt_mutex_free_waiter(&waiter);
  
  	return ret;
  }
  
  /*
   * Slow path try-lock function:
   */
  static inline int

  rt_mutex_slowtrylock(struct rt_mutex *lock)

  {
  	int ret = 0;
  
  	spin_lock(&lock->wait_lock);
  
  	if (likely(rt_mutex_owner(lock) != current)) {

  		ret = try_to_take_rt_mutex(lock);

  		/*
  		 * try_to_take_rt_mutex() sets the lock waiters
  		 * bit unconditionally. Clean this up.
  		 */
  		fixup_rt_mutex_waiters(lock);
  	}
  
  	spin_unlock(&lock->wait_lock);
  
  	return ret;
  }
  
  /*
   * Slow path to release a rt-mutex:
   */
  static void __sched
  rt_mutex_slowunlock(struct rt_mutex *lock)
  {
  	spin_lock(&lock->wait_lock);
  
  	debug_rt_mutex_unlock(lock);
  
  	rt_mutex_deadlock_account_unlock(current);
  
  	if (!rt_mutex_has_waiters(lock)) {
  		lock->owner = NULL;
  		spin_unlock(&lock->wait_lock);
  		return;
  	}
  
  	wakeup_next_waiter(lock);
  
  	spin_unlock(&lock->wait_lock);
  
  	/* Undo pi boosting if necessary: */
  	rt_mutex_adjust_prio(current);
  }
  
  /*
   * debug aware fast / slowpath lock,trylock,unlock
   *
   * The atomic acquire/release ops are compiled away, when either the
   * architecture does not support cmpxchg or when debugging is enabled.
   */
  static inline int
  rt_mutex_fastlock(struct rt_mutex *lock, int state,
  		  int detect_deadlock,
  		  int (*slowfn)(struct rt_mutex *lock, int state,
  				struct hrtimer_sleeper *timeout,

  				int detect_deadlock))

  {
  	if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
  		rt_mutex_deadlock_account_lock(lock, current);
  		return 0;
  	} else

  		return slowfn(lock, state, NULL, detect_deadlock);

  }
  
  static inline int
  rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
  			struct hrtimer_sleeper *timeout, int detect_deadlock,
  			int (*slowfn)(struct rt_mutex *lock, int state,
  				      struct hrtimer_sleeper *timeout,

  				      int detect_deadlock))

  {
  	if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
  		rt_mutex_deadlock_account_lock(lock, current);
  		return 0;
  	} else

  		return slowfn(lock, state, timeout, detect_deadlock);

  }
  
  static inline int
  rt_mutex_fasttrylock(struct rt_mutex *lock,

  		     int (*slowfn)(struct rt_mutex *lock))

  {
  	if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
  		rt_mutex_deadlock_account_lock(lock, current);
  		return 1;
  	}

  	return slowfn(lock);

  }
  
  static inline void
  rt_mutex_fastunlock(struct rt_mutex *lock,
  		    void (*slowfn)(struct rt_mutex *lock))
  {
  	if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
  		rt_mutex_deadlock_account_unlock(current);
  	else
  		slowfn(lock);
  }
  
  /**
   * rt_mutex_lock - lock a rt_mutex
   *
   * @lock: the rt_mutex to be locked
   */
  void __sched rt_mutex_lock(struct rt_mutex *lock)
  {
  	might_sleep();
  
  	rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
  }
  EXPORT_SYMBOL_GPL(rt_mutex_lock);
  
  /**
   * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
   *
   * @lock: 		the rt_mutex to be locked
   * @detect_deadlock:	deadlock detection on/off
   *
   * Returns:
   *  0 		on success
   * -EINTR 	when interrupted by a signal
   * -EDEADLK	when the lock would deadlock (when deadlock detection is on)
   */
  int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
  						 int detect_deadlock)
  {
  	might_sleep();
  
  	return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
  				 detect_deadlock, rt_mutex_slowlock);
  }
  EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
  
  /**
   * rt_mutex_lock_interruptible_ktime - lock a rt_mutex interruptible
   *				       the timeout structure is provided
   *				       by the caller
   *
   * @lock: 		the rt_mutex to be locked
   * @timeout:		timeout structure or NULL (no timeout)
   * @detect_deadlock:	deadlock detection on/off
   *
   * Returns:
   *  0 		on success
   * -EINTR 	when interrupted by a signal
   * -ETIMEOUT	when the timeout expired
   * -EDEADLK	when the lock would deadlock (when deadlock detection is on)
   */
  int
  rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
  		    int detect_deadlock)
  {
  	might_sleep();
  
  	return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
  				       detect_deadlock, rt_mutex_slowlock);
  }
  EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
  
  /**
   * rt_mutex_trylock - try to lock a rt_mutex
   *
   * @lock:	the rt_mutex to be locked
   *
   * Returns 1 on success and 0 on contention
   */
  int __sched rt_mutex_trylock(struct rt_mutex *lock)
  {
  	return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
  }
  EXPORT_SYMBOL_GPL(rt_mutex_trylock);
  
  /**
   * rt_mutex_unlock - unlock a rt_mutex
   *
   * @lock: the rt_mutex to be unlocked
   */
  void __sched rt_mutex_unlock(struct rt_mutex *lock)
  {
  	rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
  }
  EXPORT_SYMBOL_GPL(rt_mutex_unlock);
  
  /***
   * rt_mutex_destroy - mark a mutex unusable
   * @lock: the mutex to be destroyed
   *
   * This function marks the mutex uninitialized, and any subsequent
   * use of the mutex is forbidden. The mutex must not be locked when
   * this function is called.
   */
  void rt_mutex_destroy(struct rt_mutex *lock)
  {
  	WARN_ON(rt_mutex_is_locked(lock));
  #ifdef CONFIG_DEBUG_RT_MUTEXES
  	lock->magic = NULL;
  #endif
  }
  
  EXPORT_SYMBOL_GPL(rt_mutex_destroy);
  
  /**
   * __rt_mutex_init - initialize the rt lock
   *
   * @lock: the rt lock to be initialized
   *
   * Initialize the rt lock to unlocked state.
   *
   * Initializing of a locked rt lock is not allowed
   */
  void __rt_mutex_init(struct rt_mutex *lock, const char *name)
  {
  	lock->owner = NULL;
  	spin_lock_init(&lock->wait_lock);
  	plist_head_init(&lock->wait_list, &lock->wait_lock);
  
  	debug_rt_mutex_init(lock, name);
  }
  EXPORT_SYMBOL_GPL(__rt_mutex_init);

  
  /**
   * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
   *				proxy owner
   *
   * @lock: 	the rt_mutex to be locked
   * @proxy_owner:the task to set as owner
   *
   * No locking. Caller has to do serializing itself
   * Special API call for PI-futex support
   */
  void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
  				struct task_struct *proxy_owner)
  {
  	__rt_mutex_init(lock, NULL);

  	debug_rt_mutex_proxy_lock(lock, proxy_owner);

  	rt_mutex_set_owner(lock, proxy_owner, 0);
  	rt_mutex_deadlock_account_lock(lock, proxy_owner);
  }
  
  /**
   * rt_mutex_proxy_unlock - release a lock on behalf of owner
   *
   * @lock: 	the rt_mutex to be locked
   *
   * No locking. Caller has to do serializing itself
   * Special API call for PI-futex support
   */
  void rt_mutex_proxy_unlock(struct rt_mutex *lock,
  			   struct task_struct *proxy_owner)
  {
  	debug_rt_mutex_proxy_unlock(lock);
  	rt_mutex_set_owner(lock, NULL, 0);
  	rt_mutex_deadlock_account_unlock(proxy_owner);
  }
  
  /**
   * rt_mutex_next_owner - return the next owner of the lock
   *
   * @lock: the rt lock query
   *
   * Returns the next owner of the lock or NULL
   *
   * Caller has to serialize against other accessors to the lock
   * itself.
   *
   * Special API call for PI-futex support
   */
  struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
  {
  	if (!rt_mutex_has_waiters(lock))
  		return NULL;
  
  	return rt_mutex_top_waiter(lock)->task;
  }