/*
   * 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/locking/rt-mutex-design.txt for details.

   */
  #include <linux/spinlock.h>

  #include <linux/export.h>

  #include <linux/sched/signal.h>

  #include <linux/sched/rt.h>

  #include <linux/sched/deadline.h>

  #include <linux/sched/wake_q.h>

  #include <linux/sched/debug.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
   * is used to keep track of the "lock has waiters" state.

   *

   * owner	bit0
   * NULL		0	lock is free (fast acquire possible)
   * NULL		1	lock is free and has waiters and the top waiter
   *				is going to take the lock*
   * taskpointer	0	lock is held (fast release possible)
   * taskpointer	1	lock is held and has waiters**

   *
   * The fast atomic compare exchange based acquire and release is only

   * possible when bit 0 of lock->owner is 0.
   *
   * (*) It also can be a transitional state when grabbing the lock
   * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
   * we need to set the bit0 before looking at the lock, and the owner may be
   * NULL in this small time, hence this can be a transitional state.

   *

   * (**) There is a small time when bit 0 is set but there are no
   * waiters. This can happen when grabbing the lock in the slow path.
   * To prevent a cmpxchg of the owner releasing the lock, we need to
   * set this bit before looking at the lock.

   */

  static void

  rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)

  {

  	unsigned long val = (unsigned long)owner;

  
  	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)
  {

  	unsigned long owner, *p = (unsigned long *) &lock->owner;
  
  	if (rt_mutex_has_waiters(lock))
  		return;
  
  	/*
  	 * The rbtree has no waiters enqueued, now make sure that the
  	 * lock->owner still has the waiters bit set, otherwise the
  	 * following can happen:
  	 *
  	 * CPU 0	CPU 1		CPU2
  	 * l->owner=T1
  	 *		rt_mutex_lock(l)
  	 *		lock(l->lock)
  	 *		l->owner = T1 | HAS_WAITERS;
  	 *		enqueue(T2)
  	 *		boost()
  	 *		  unlock(l->lock)
  	 *		block()
  	 *
  	 *				rt_mutex_lock(l)
  	 *				lock(l->lock)
  	 *				l->owner = T1 | HAS_WAITERS;
  	 *				enqueue(T3)
  	 *				boost()
  	 *				  unlock(l->lock)
  	 *				block()
  	 *		signal(->T2)	signal(->T3)
  	 *		lock(l->lock)
  	 *		dequeue(T2)
  	 *		deboost()
  	 *		  unlock(l->lock)
  	 *				lock(l->lock)
  	 *				dequeue(T3)
  	 *				 ==> wait list is empty
  	 *				deboost()
  	 *				 unlock(l->lock)
  	 *		lock(l->lock)
  	 *		fixup_rt_mutex_waiters()
  	 *		  if (wait_list_empty(l) {
  	 *		    l->owner = owner
  	 *		    owner = l->owner & ~HAS_WAITERS;
  	 *		      ==> l->owner = T1
  	 *		  }
  	 *				lock(l->lock)
  	 * rt_mutex_unlock(l)		fixup_rt_mutex_waiters()
  	 *				  if (wait_list_empty(l) {
  	 *				    owner = l->owner & ~HAS_WAITERS;
  	 * cmpxchg(l->owner, T1, NULL)
  	 *  ===> Success (l->owner = NULL)
  	 *
  	 *				    l->owner = owner
  	 *				      ==> l->owner = T1
  	 *				  }
  	 *
  	 * With the check for the waiter bit in place T3 on CPU2 will not
  	 * overwrite. All tasks fiddling with the waiters bit are
  	 * serialized by l->lock, so nothing else can modify the waiters
  	 * bit. If the bit is set then nothing can change l->owner either
  	 * so the simple RMW is safe. The cmpxchg() will simply fail if it
  	 * happens in the middle of the RMW because the waiters bit is
  	 * still set.
  	 */
  	owner = READ_ONCE(*p);
  	if (owner & RT_MUTEX_HAS_WAITERS)
  		WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);

  }
  
  /*

   * We can speed up the acquire/release, if there's no debugging state to be
   * set up.

   */

  #ifndef CONFIG_DEBUG_RT_MUTEXES

  # define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
  # define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
  # define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
  
  /*
   * Callers must hold the ->wait_lock -- which is the whole purpose as we force
   * all future threads that attempt to [Rmw] the lock to the slowpath. As such
   * relaxed semantics suffice.
   */

  static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  {
  	unsigned long owner, *p = (unsigned long *) &lock->owner;
  
  	do {
  		owner = *p;

  	} while (cmpxchg_relaxed(p, owner,
  				 owner | RT_MUTEX_HAS_WAITERS) != owner);

  }

  
  /*
   * Safe fastpath aware unlock:
   * 1) Clear the waiters bit
   * 2) Drop lock->wait_lock
   * 3) Try to unlock the lock with cmpxchg
   */

  static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
  					unsigned long flags)

  	__releases(lock->wait_lock)
  {
  	struct task_struct *owner = rt_mutex_owner(lock);
  
  	clear_rt_mutex_waiters(lock);

  	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

  	/*
  	 * If a new waiter comes in between the unlock and the cmpxchg
  	 * we have two situations:
  	 *
  	 * unlock(wait_lock);
  	 *					lock(wait_lock);
  	 * cmpxchg(p, owner, 0) == owner
  	 *					mark_rt_mutex_waiters(lock);
  	 *					acquire(lock);
  	 * or:
  	 *
  	 * unlock(wait_lock);
  	 *					lock(wait_lock);
  	 *					mark_rt_mutex_waiters(lock);
  	 *
  	 * cmpxchg(p, owner, 0) != owner
  	 *					enqueue_waiter();
  	 *					unlock(wait_lock);
  	 * lock(wait_lock);
  	 * wake waiter();
  	 * unlock(wait_lock);
  	 *					lock(wait_lock);
  	 *					acquire(lock);
  	 */

  	return rt_mutex_cmpxchg_release(lock, owner, NULL);

  }

  #else

  # define rt_mutex_cmpxchg_relaxed(l,c,n)	(0)
  # define rt_mutex_cmpxchg_acquire(l,c,n)	(0)
  # define rt_mutex_cmpxchg_release(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);
  }

  
  /*
   * Simple slow path only version: lock->owner is protected by lock->wait_lock.
   */

  static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
  					unsigned long flags)

  	__releases(lock->wait_lock)
  {
  	lock->owner = NULL;

  	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

  	return true;
  }

  #endif

  /*
   * Only use with rt_mutex_waiter_{less,equal}()
   */
  #define task_to_waiter(p)	\
  	&(struct rt_mutex_waiter){ .prio = (p)->prio, .deadline = (p)->dl.deadline }

  static inline int
  rt_mutex_waiter_less(struct rt_mutex_waiter *left,
  		     struct rt_mutex_waiter *right)
  {

  	if (left->prio < right->prio)

  		return 1;
  
  	/*

  	 * If both waiters have dl_prio(), we check the deadlines of the
  	 * associated tasks.
  	 * If left waiter has a dl_prio(), and we didn't return 1 above,
  	 * then right waiter has a dl_prio() too.

  	 */

  	if (dl_prio(left->prio))

  		return dl_time_before(left->deadline, right->deadline);

  
  	return 0;
  }

  static inline int
  rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
  		      struct rt_mutex_waiter *right)
  {
  	if (left->prio != right->prio)
  		return 0;
  
  	/*
  	 * If both waiters have dl_prio(), we check the deadlines of the
  	 * associated tasks.
  	 * If left waiter has a dl_prio(), and we didn't return 0 above,
  	 * then right waiter has a dl_prio() too.
  	 */
  	if (dl_prio(left->prio))
  		return left->deadline == right->deadline;
  
  	return 1;
  }

  static void
  rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
  {

  	struct rb_node **link = &lock->waiters.rb_root.rb_node;

  	struct rb_node *parent = NULL;
  	struct rt_mutex_waiter *entry;

  	bool leftmost = true;

  
  	while (*link) {
  		parent = *link;
  		entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
  		if (rt_mutex_waiter_less(waiter, entry)) {
  			link = &parent->rb_left;
  		} else {
  			link = &parent->rb_right;

  			leftmost = false;

  		}
  	}

  	rb_link_node(&waiter->tree_entry, parent, link);

  	rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);

  }
  
  static void
  rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
  {
  	if (RB_EMPTY_NODE(&waiter->tree_entry))
  		return;

  	rb_erase_cached(&waiter->tree_entry, &lock->waiters);

  	RB_CLEAR_NODE(&waiter->tree_entry);
  }
  
  static void
  rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
  {

  	struct rb_node **link = &task->pi_waiters.rb_root.rb_node;

  	struct rb_node *parent = NULL;
  	struct rt_mutex_waiter *entry;

  	bool leftmost = true;

  
  	while (*link) {
  		parent = *link;
  		entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
  		if (rt_mutex_waiter_less(waiter, entry)) {
  			link = &parent->rb_left;
  		} else {
  			link = &parent->rb_right;

  			leftmost = false;

  		}
  	}

  	rb_link_node(&waiter->pi_tree_entry, parent, link);

  	rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);

  }
  
  static void
  rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
  {
  	if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
  		return;

  	rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);

  	RB_CLEAR_NODE(&waiter->pi_tree_entry);
  }

  static void rt_mutex_adjust_prio(struct task_struct *p)

  {

  	struct task_struct *pi_task = NULL;

  	lockdep_assert_held(&p->pi_lock);

  	if (task_has_pi_waiters(p))
  		pi_task = task_top_pi_waiter(p)->task;

  	rt_mutex_setprio(p, pi_task);

  }
  
  /*

   * Deadlock detection is conditional:
   *
   * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
   * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
   *
   * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
   * conducted independent of the detect argument.
   *
   * If the waiter argument is NULL this indicates the deboost path and
   * deadlock detection is disabled independent of the detect argument
   * and the config settings.
   */
  static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
  					  enum rtmutex_chainwalk chwalk)
  {
  	/*
  	 * This is just a wrapper function for the following call,
  	 * because debug_rt_mutex_detect_deadlock() smells like a magic
  	 * debug feature and I wanted to keep the cond function in the
  	 * main source file along with the comments instead of having
  	 * two of the same in the headers.
  	 */
  	return debug_rt_mutex_detect_deadlock(waiter, chwalk);
  }
  
  /*

   * Max number of times we'll walk the boosting chain:
   */
  int max_lock_depth = 1024;

  static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
  {
  	return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
  }

  /*
   * Adjust the priority chain. Also used for deadlock detection.
   * Decreases task's usage by one - may thus free the task.

   *

   * @task:	the task owning the mutex (owner) for which a chain walk is
   *		probably needed

   * @chwalk:	do we have to carry out deadlock detection?

   * @orig_lock:	the mutex (can be NULL if we are walking the chain to recheck
   *		things for a task that has just got its priority adjusted, and
   *		is waiting on a mutex)
   * @next_lock:	the mutex on which the owner of @orig_lock was blocked before
   *		we dropped its pi_lock. Is never dereferenced, only used for
   *		comparison to detect lock chain changes.

   * @orig_waiter: rt_mutex_waiter struct for the task that has just donated

   *		its priority to the mutex owner (can be NULL in the case
   *		depicted above or if the top waiter is gone away and we are
   *		actually deboosting the owner)
   * @top_task:	the current top waiter

   *

   * Returns 0 or -EDEADLK.

   *
   * Chain walk basics and protection scope
   *
   * [R] refcount on task
   * [P] task->pi_lock held
   * [L] rtmutex->wait_lock held
   *
   * Step	Description				Protected by
   *	function arguments:
   *	@task					[R]
   *	@orig_lock if != NULL			@top_task is blocked on it
   *	@next_lock				Unprotected. Cannot be
   *						dereferenced. Only used for
   *						comparison.
   *	@orig_waiter if != NULL			@top_task is blocked on it
   *	@top_task				current, or in case of proxy
   *						locking protected by calling
   *						code
   *	again:
   *	  loop_sanity_check();
   *	retry:
   * [1]	  lock(task->pi_lock);			[R] acquire [P]
   * [2]	  waiter = task->pi_blocked_on;		[P]
   * [3]	  check_exit_conditions_1();		[P]
   * [4]	  lock = waiter->lock;			[P]
   * [5]	  if (!try_lock(lock->wait_lock)) {	[P] try to acquire [L]
   *	    unlock(task->pi_lock);		release [P]
   *	    goto retry;
   *	  }
   * [6]	  check_exit_conditions_2();		[P] + [L]
   * [7]	  requeue_lock_waiter(lock, waiter);	[P] + [L]
   * [8]	  unlock(task->pi_lock);		release [P]
   *	  put_task_struct(task);		release [R]
   * [9]	  check_exit_conditions_3();		[L]
   * [10]	  task = owner(lock);			[L]
   *	  get_task_struct(task);		[L] acquire [R]
   *	  lock(task->pi_lock);			[L] acquire [P]
   * [11]	  requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
   * [12]	  check_exit_conditions_4();		[P] + [L]
   * [13]	  unlock(task->pi_lock);		release [P]
   *	  unlock(lock->wait_lock);		release [L]
   *	  goto again;

   */

  static int rt_mutex_adjust_prio_chain(struct task_struct *task,

  				      enum rtmutex_chainwalk chwalk,

  				      struct rt_mutex *orig_lock,

  				      struct rt_mutex *next_lock,

  				      struct rt_mutex_waiter *orig_waiter,
  				      struct task_struct *top_task)

  {

  	struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;

  	struct rt_mutex_waiter *prerequeue_top_waiter;

  	int ret = 0, depth = 0;

  	struct rt_mutex *lock;

  	bool detect_deadlock;

  	bool requeue = true;

  	detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);

  
  	/*
  	 * 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:

  	/*
  	 * We limit the lock chain length for each invocation.
  	 */

  	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 -EDEADLK;

  	}

  
  	/*
  	 * We are fully preemptible here and only hold the refcount on
  	 * @task. So everything can have changed under us since the
  	 * caller or our own code below (goto retry/again) dropped all
  	 * locks.
  	 */

   retry:
  	/*

  	 * [1] Task cannot go away as we did a get_task() before !

  	 */

  	raw_spin_lock_irq(&task->pi_lock);

  	/*
  	 * [2] Get the waiter on which @task is blocked on.
  	 */

  	waiter = task->pi_blocked_on;

  
  	/*
  	 * [3] check_exit_conditions_1() protected by task->pi_lock.
  	 */

  	/*
  	 * 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)

  		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.

  	 */

  	if (orig_waiter && !rt_mutex_owner(orig_lock))

  		goto out_unlock_pi;
  
  	/*

  	 * We dropped all locks after taking a refcount on @task, so
  	 * the task might have moved on in the lock chain or even left
  	 * the chain completely and blocks now on an unrelated lock or
  	 * on @orig_lock.
  	 *
  	 * We stored the lock on which @task was blocked in @next_lock,
  	 * so we can detect the chain change.
  	 */
  	if (next_lock != waiter->lock)
  		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) {
  		if (!task_has_pi_waiters(task))
  			goto out_unlock_pi;
  		/*
  		 * If deadlock detection is off, we stop here if we

  		 * are not the top pi waiter of the task. If deadlock
  		 * detection is enabled we continue, but stop the
  		 * requeueing in the chain walk.

  		 */

  		if (top_waiter != task_top_pi_waiter(task)) {
  			if (!detect_deadlock)
  				goto out_unlock_pi;
  			else
  				requeue = false;
  		}

  	}

  
  	/*

  	 * If the waiter priority is the same as the task priority
  	 * then there is no further priority adjustment necessary.  If
  	 * deadlock detection is off, we stop the chain walk. If its
  	 * enabled we continue, but stop the requeueing in the chain
  	 * walk.

  	 */

  	if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {

  		if (!detect_deadlock)
  			goto out_unlock_pi;
  		else
  			requeue = false;
  	}

  	/*
  	 * [4] Get the next lock
  	 */

  	lock = waiter->lock;

  	/*
  	 * [5] We need to trylock here as we are holding task->pi_lock,
  	 * which is the reverse lock order versus the other rtmutex
  	 * operations.
  	 */

  	if (!raw_spin_trylock(&lock->wait_lock)) {

  		raw_spin_unlock_irq(&task->pi_lock);

  		cpu_relax();
  		goto retry;
  	}

  	/*

  	 * [6] check_exit_conditions_2() protected by task->pi_lock and
  	 * lock->wait_lock.
  	 *

  	 * Deadlock detection. If the lock is the same as the original
  	 * lock which caused us to walk the lock chain or if the
  	 * current lock is owned by the task which initiated the chain
  	 * walk, we detected a deadlock.
  	 */

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

  		debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);

  		raw_spin_unlock(&lock->wait_lock);

  		ret = -EDEADLK;

  		goto out_unlock_pi;
  	}

  	/*

  	 * If we just follow the lock chain for deadlock detection, no
  	 * need to do all the requeue operations. To avoid a truckload
  	 * of conditionals around the various places below, just do the
  	 * minimum chain walk checks.
  	 */
  	if (!requeue) {
  		/*
  		 * No requeue[7] here. Just release @task [8]
  		 */

  		raw_spin_unlock(&task->pi_lock);

  		put_task_struct(task);
  
  		/*
  		 * [9] check_exit_conditions_3 protected by lock->wait_lock.
  		 * If there is no owner of the lock, end of chain.
  		 */
  		if (!rt_mutex_owner(lock)) {

  			raw_spin_unlock_irq(&lock->wait_lock);

  			return 0;
  		}
  
  		/* [10] Grab the next task, i.e. owner of @lock */
  		task = rt_mutex_owner(lock);
  		get_task_struct(task);

  		raw_spin_lock(&task->pi_lock);

  
  		/*
  		 * No requeue [11] here. We just do deadlock detection.
  		 *
  		 * [12] Store whether owner is blocked
  		 * itself. Decision is made after dropping the locks
  		 */
  		next_lock = task_blocked_on_lock(task);
  		/*
  		 * Get the top waiter for the next iteration
  		 */
  		top_waiter = rt_mutex_top_waiter(lock);
  
  		/* [13] Drop locks */

  		raw_spin_unlock(&task->pi_lock);
  		raw_spin_unlock_irq(&lock->wait_lock);

  
  		/* If owner is not blocked, end of chain. */
  		if (!next_lock)
  			goto out_put_task;
  		goto again;
  	}
  
  	/*

  	 * Store the current top waiter before doing the requeue
  	 * operation on @lock. We need it for the boost/deboost
  	 * decision below.
  	 */
  	prerequeue_top_waiter = rt_mutex_top_waiter(lock);

  	/* [7] Requeue the waiter in the lock waiter tree. */

  	rt_mutex_dequeue(lock, waiter);

  
  	/*
  	 * Update the waiter prio fields now that we're dequeued.
  	 *
  	 * These values can have changed through either:
  	 *
  	 *   sys_sched_set_scheduler() / sys_sched_setattr()
  	 *
  	 * or
  	 *
  	 *   DL CBS enforcement advancing the effective deadline.
  	 *
  	 * Even though pi_waiters also uses these fields, and that tree is only
  	 * updated in [11], we can do this here, since we hold [L], which
  	 * serializes all pi_waiters access and rb_erase() does not care about
  	 * the values of the node being removed.
  	 */

  	waiter->prio = task->prio;

  	waiter->deadline = task->dl.deadline;

  	rt_mutex_enqueue(lock, waiter);

  	/* [8] Release the task */

  	raw_spin_unlock(&task->pi_lock);

  	put_task_struct(task);

  	/*

  	 * [9] check_exit_conditions_3 protected by lock->wait_lock.
  	 *

  	 * We must abort the chain walk if there is no lock owner even
  	 * in the dead lock detection case, as we have nothing to
  	 * follow here. This is the end of the chain we are walking.
  	 */

  	if (!rt_mutex_owner(lock)) {
  		/*

  		 * If the requeue [7] above changed the top waiter,
  		 * then we need to wake the new top waiter up to try
  		 * to get the lock.

  		 */

  		if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))

  			wake_up_process(rt_mutex_top_waiter(lock)->task);

  		raw_spin_unlock_irq(&lock->wait_lock);

  		return 0;

  	}

  	/* [10] Grab the next task, i.e. the owner of @lock */

  	task = rt_mutex_owner(lock);

  	get_task_struct(task);

  	raw_spin_lock(&task->pi_lock);

  	/* [11] requeue the pi waiters if necessary */

  	if (waiter == rt_mutex_top_waiter(lock)) {

  		/*
  		 * The waiter became the new top (highest priority)
  		 * waiter on the lock. Replace the previous top waiter

  		 * in the owner tasks pi waiters tree with this waiter

  		 * and adjust the priority of the owner.
  		 */
  		rt_mutex_dequeue_pi(task, prerequeue_top_waiter);

  		rt_mutex_enqueue_pi(task, waiter);

  		rt_mutex_adjust_prio(task);

  	} else if (prerequeue_top_waiter == waiter) {
  		/*
  		 * The waiter was the top waiter on the lock, but is
  		 * no longer the top prority waiter. Replace waiter in

  		 * the owner tasks pi waiters tree with the new top

  		 * (highest priority) waiter and adjust the priority
  		 * of the owner.
  		 * The new top waiter is stored in @waiter so that
  		 * @waiter == @top_waiter evaluates to true below and
  		 * we continue to deboost the rest of the chain.
  		 */

  		rt_mutex_dequeue_pi(task, waiter);

  		waiter = rt_mutex_top_waiter(lock);

  		rt_mutex_enqueue_pi(task, waiter);

  		rt_mutex_adjust_prio(task);

  	} else {
  		/*
  		 * Nothing changed. No need to do any priority
  		 * adjustment.
  		 */

  	}

  	/*

  	 * [12] check_exit_conditions_4() protected by task->pi_lock
  	 * and lock->wait_lock. The actual decisions are made after we
  	 * dropped the locks.
  	 *

  	 * Check whether the task which owns the current lock is pi
  	 * blocked itself. If yes we store a pointer to the lock for
  	 * the lock chain change detection above. After we dropped
  	 * task->pi_lock next_lock cannot be dereferenced anymore.
  	 */
  	next_lock = task_blocked_on_lock(task);

  	/*
  	 * Store the top waiter of @lock for the end of chain walk
  	 * decision below.
  	 */

  	top_waiter = rt_mutex_top_waiter(lock);

  
  	/* [13] Drop the locks */

  	raw_spin_unlock(&task->pi_lock);
  	raw_spin_unlock_irq(&lock->wait_lock);

  	/*

  	 * Make the actual exit decisions [12], based on the stored
  	 * values.
  	 *

  	 * We reached the end of the lock chain. Stop right here. No
  	 * point to go back just to figure that out.
  	 */
  	if (!next_lock)
  		goto out_put_task;

  	/*
  	 * If the current waiter is not the top waiter on the lock,
  	 * then we can stop the chain walk here if we are not in full
  	 * deadlock detection mode.
  	 */

  	if (!detect_deadlock && waiter != top_waiter)
  		goto out_put_task;
  
  	goto again;
  
   out_unlock_pi:

  	raw_spin_unlock_irq(&task->pi_lock);

   out_put_task:
  	put_task_struct(task);

  	return ret;
  }
  
  /*

   * Try to take an rt-mutex
   *

   * Must be called with lock->wait_lock held and interrupts disabled

   *

   * @lock:   The lock to be acquired.
   * @task:   The task which wants to acquire the lock

   * @waiter: The waiter that is queued to the lock's wait tree if the

   *	    callsite called task_blocked_on_lock(), otherwise NULL

   */

  static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,

  				struct rt_mutex_waiter *waiter)

  {

  	lockdep_assert_held(&lock->wait_lock);

  	/*

  	 * Before testing whether we can acquire @lock, we set the
  	 * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
  	 * other tasks which try to modify @lock into the slow path
  	 * and they serialize on @lock->wait_lock.

  	 *

  	 * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
  	 * as explained at the top of this file if and only if:

  	 *

  	 * - There is a lock owner. The caller must fixup the
  	 *   transient state if it does a trylock or leaves the lock
  	 *   function due to a signal or timeout.
  	 *
  	 * - @task acquires the lock and there are no other
  	 *   waiters. This is undone in rt_mutex_set_owner(@task) at
  	 *   the end of this function.

  	 */
  	mark_rt_mutex_waiters(lock);

  	/*
  	 * If @lock has an owner, give up.
  	 */

  	if (rt_mutex_owner(lock))

  		return 0;

  	/*

  	 * If @waiter != NULL, @task has already enqueued the waiter

  	 * into @lock waiter tree. If @waiter == NULL then this is a

  	 * trylock attempt.

  	 */

  	if (waiter) {
  		/*
  		 * If waiter is not the highest priority waiter of
  		 * @lock, give up.
  		 */
  		if (waiter != rt_mutex_top_waiter(lock))
  			return 0;

  		/*
  		 * We can acquire the lock. Remove the waiter from the

  		 * lock waiters tree.

  		 */
  		rt_mutex_dequeue(lock, waiter);

  	} else {

  		/*

  		 * If the lock has waiters already we check whether @task is
  		 * eligible to take over the lock.
  		 *
  		 * If there are no other waiters, @task can acquire
  		 * the lock.  @task->pi_blocked_on is NULL, so it does
  		 * not need to be dequeued.

  		 */
  		if (rt_mutex_has_waiters(lock)) {

  			/*
  			 * If @task->prio is greater than or equal to
  			 * the top waiter priority (kernel view),
  			 * @task lost.
  			 */

  			if (!rt_mutex_waiter_less(task_to_waiter(task),
  						  rt_mutex_top_waiter(lock)))

  				return 0;
  
  			/*
  			 * The current top waiter stays enqueued. We
  			 * don't have to change anything in the lock
  			 * waiters order.
  			 */
  		} else {
  			/*
  			 * No waiters. Take the lock without the
  			 * pi_lock dance.@task->pi_blocked_on is NULL
  			 * and we have no waiters to enqueue in @task

  			 * pi waiters tree.

  			 */
  			goto takeit;

  		}

  	}

  	/*
  	 * Clear @task->pi_blocked_on. Requires protection by
  	 * @task->pi_lock. Redundant operation for the @waiter == NULL
  	 * case, but conditionals are more expensive than a redundant
  	 * store.
  	 */

  	raw_spin_lock(&task->pi_lock);

  	task->pi_blocked_on = NULL;
  	/*
  	 * Finish the lock acquisition. @task is the new owner. If
  	 * other waiters exist we have to insert the highest priority

  	 * waiter into @task->pi_waiters tree.

  	 */
  	if (rt_mutex_has_waiters(lock))
  		rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));

  	raw_spin_unlock(&task->pi_lock);

  
  takeit:

  	/* We got the lock. */

  	debug_rt_mutex_lock(lock);

  	/*
  	 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
  	 * are still waiters or clears it.
  	 */

  	rt_mutex_set_owner(lock, task);

  	return 1;
  }
  
  /*
   * Task blocks on lock.
   *
   * Prepare waiter and propagate pi chain
   *

   * This must be called with lock->wait_lock held and interrupts disabled

   */
  static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
  				   struct rt_mutex_waiter *waiter,

  				   struct task_struct *task,

  				   enum rtmutex_chainwalk chwalk)

  {

  	struct task_struct *owner = rt_mutex_owner(lock);

  	struct rt_mutex_waiter *top_waiter = waiter;

  	struct rt_mutex *next_lock;

  	int chain_walk = 0, res;

  	lockdep_assert_held(&lock->wait_lock);

  	/*
  	 * Early deadlock detection. We really don't want the task to
  	 * enqueue on itself just to untangle the mess later. It's not
  	 * only an optimization. We drop the locks, so another waiter
  	 * can come in before the chain walk detects the deadlock. So
  	 * the other will detect the deadlock and return -EDEADLOCK,
  	 * which is wrong, as the other waiter is not in a deadlock
  	 * situation.
  	 */

  	if (owner == task)

  		return -EDEADLK;

  	raw_spin_lock(&task->pi_lock);

  	waiter->task = task;

  	waiter->lock = lock;

  	waiter->prio = task->prio;

  	waiter->deadline = task->dl.deadline;

  
  	/* Get the top priority waiter on the lock */
  	if (rt_mutex_has_waiters(lock))
  		top_waiter = rt_mutex_top_waiter(lock);

  	rt_mutex_enqueue(lock, waiter);

  	task->pi_blocked_on = waiter;

  	raw_spin_unlock(&task->pi_lock);

  	if (!owner)
  		return 0;

  	raw_spin_lock(&owner->pi_lock);

  	if (waiter == rt_mutex_top_waiter(lock)) {

  		rt_mutex_dequeue_pi(owner, top_waiter);
  		rt_mutex_enqueue_pi(owner, waiter);

  		rt_mutex_adjust_prio(owner);

  		if (owner->pi_blocked_on)
  			chain_walk = 1;

  	} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {

  		chain_walk = 1;

  	}

  	/* Store the lock on which owner is blocked or NULL */
  	next_lock = task_blocked_on_lock(owner);

  	raw_spin_unlock(&owner->pi_lock);

  	/*
  	 * Even if full deadlock detection is on, if the owner is not
  	 * blocked itself, we can avoid finding this out in the chain
  	 * walk.
  	 */
  	if (!chain_walk || !next_lock)

  		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);

  	raw_spin_unlock_irq(&lock->wait_lock);

  	res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,

  					 next_lock, waiter, task);

  	raw_spin_lock_irq(&lock->wait_lock);

  
  	return res;
  }
  
  /*

   * Remove the top waiter from the current tasks pi waiter tree and

   * queue it up.

   *

   * Called with lock->wait_lock held and interrupts disabled.

   */

  static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
  				    struct rt_mutex *lock)

  {
  	struct rt_mutex_waiter *waiter;

  	raw_spin_lock(&current->pi_lock);

  
  	waiter = rt_mutex_top_waiter(lock);

  
  	/*

  	 * Remove it from current->pi_waiters and deboost.
  	 *
  	 * We must in fact deboost here in order to ensure we call
  	 * rt_mutex_setprio() to update p->pi_top_task before the
  	 * task unblocks.

  	 */

  	rt_mutex_dequeue_pi(current, waiter);

  	rt_mutex_adjust_prio(current);

  	/*
  	 * As we are waking up the top waiter, and the waiter stays
  	 * queued on the lock until it gets the lock, this lock
  	 * obviously has waiters. Just set the bit here and this has
  	 * the added benefit of forcing all new tasks into the
  	 * slow path making sure no task of lower priority than
  	 * the top waiter can steal this lock.
  	 */
  	lock->owner = (void *) RT_MUTEX_HAS_WAITERS;

  	/*
  	 * We deboosted before waking the top waiter task such that we don't
  	 * run two tasks with the 'same' priority (and ensure the
  	 * p->pi_top_task pointer points to a blocked task). This however can
  	 * lead to priority inversion if we would get preempted after the
  	 * deboost but before waking our donor task, hence the preempt_disable()
  	 * before unlock.
  	 *
  	 * Pairs with preempt_enable() in rt_mutex_postunlock();
  	 */
  	preempt_disable();

  	wake_q_add(wake_q, waiter->task);

  	raw_spin_unlock(&current->pi_lock);

  }
  
  /*

   * Remove a waiter from a lock and give up

   *

   * Must be called with lock->wait_lock held and interrupts disabled. I must

   * have just failed to try_to_take_rt_mutex().

   */

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

  {

  	bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));

  	struct task_struct *owner = rt_mutex_owner(lock);

  	struct rt_mutex *next_lock;

  	lockdep_assert_held(&lock->wait_lock);

  	raw_spin_lock(&current->pi_lock);

  	rt_mutex_dequeue(lock, waiter);

  	current->pi_blocked_on = NULL;

  	raw_spin_unlock(&current->pi_lock);

  	/*
  	 * Only update priority if the waiter was the highest priority
  	 * waiter of the lock and there is an owner to update.
  	 */
  	if (!owner || !is_top_waiter)

  		return;

  	raw_spin_lock(&owner->pi_lock);

  	rt_mutex_dequeue_pi(owner, waiter);

  	if (rt_mutex_has_waiters(lock))
  		rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));

  	rt_mutex_adjust_prio(owner);

  	/* Store the lock on which owner is blocked or NULL */
  	next_lock = task_blocked_on_lock(owner);

  	raw_spin_unlock(&owner->pi_lock);

  	/*
  	 * Don't walk the chain, if the owner task is not blocked
  	 * itself.
  	 */

  	if (!next_lock)

  		return;

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

  	raw_spin_unlock_irq(&lock->wait_lock);

  	rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
  				   next_lock, NULL, current);

  	raw_spin_lock_irq(&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;

  	struct rt_mutex *next_lock;

  	unsigned long flags;

  	raw_spin_lock_irqsave(&task->pi_lock, flags);

  
  	waiter = task->pi_blocked_on;

  	if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {

  		raw_spin_unlock_irqrestore(&task->pi_lock, flags);

  		return;
  	}

  	next_lock = waiter->lock;

  	raw_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, RT_MUTEX_MIN_CHAINWALK, NULL,
  				   next_lock, NULL, task);

  }

  void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
  {
  	debug_rt_mutex_init_waiter(waiter);
  	RB_CLEAR_NODE(&waiter->pi_tree_entry);
  	RB_CLEAR_NODE(&waiter->tree_entry);
  	waiter->task = NULL;
  }

  /**
   * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
   * @lock:		 the rt_mutex to take
   * @state:		 the state the task should block in (TASK_INTERRUPTIBLE

   *			 or TASK_UNINTERRUPTIBLE)

   * @timeout:		 the pre-initialized and started timer, or NULL for none
   * @waiter:		 the pre-initialized rt_mutex_waiter

   *

   * Must be called with lock->wait_lock held and interrupts disabled

   */
  static int __sched

  __rt_mutex_slowlock(struct rt_mutex *lock, int state,
  		    struct hrtimer_sleeper *timeout,

  		    struct rt_mutex_waiter *waiter)

  {

  	int ret = 0;

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

  		if (try_to_take_rt_mutex(lock, current, waiter))

  			break;
  
  		/*
  		 * TASK_INTERRUPTIBLE checks for signals and
  		 * timeout. Ignored otherwise.
  		 */

  		if (likely(state == TASK_INTERRUPTIBLE)) {

  			/* Signal pending? */
  			if (signal_pending(current))
  				ret = -EINTR;
  			if (timeout && !timeout->task)
  				ret = -ETIMEDOUT;
  			if (ret)
  				break;
  		}

  		raw_spin_unlock_irq(&lock->wait_lock);

  		debug_rt_mutex_print_deadlock(waiter);

  		schedule();

  		raw_spin_lock_irq(&lock->wait_lock);

  		set_current_state(state);
  	}

  	__set_current_state(TASK_RUNNING);

  	return ret;
  }

  static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
  				     struct rt_mutex_waiter *w)
  {
  	/*
  	 * If the result is not -EDEADLOCK or the caller requested
  	 * deadlock detection, nothing to do here.
  	 */
  	if (res != -EDEADLOCK || detect_deadlock)
  		return;
  
  	/*
  	 * Yell lowdly and stop the task right here.
  	 */
  	rt_mutex_print_deadlock(w);
  	while (1) {
  		set_current_state(TASK_INTERRUPTIBLE);
  		schedule();
  	}
  }

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

  		  enum rtmutex_chainwalk chwalk)

  {
  	struct rt_mutex_waiter waiter;

  	unsigned long flags;

  	int ret = 0;

  	rt_mutex_init_waiter(&waiter);

  	/*
  	 * Technically we could use raw_spin_[un]lock_irq() here, but this can
  	 * be called in early boot if the cmpxchg() fast path is disabled
  	 * (debug, no architecture support). In this case we will acquire the
  	 * rtmutex with lock->wait_lock held. But we cannot unconditionally
  	 * enable interrupts in that early boot case. So we need to use the
  	 * irqsave/restore variants.
  	 */
  	raw_spin_lock_irqsave(&lock->wait_lock, flags);

  
  	/* Try to acquire the lock again: */

  	if (try_to_take_rt_mutex(lock, current, NULL)) {

  		raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

  		return 0;
  	}
  
  	set_current_state(state);
  
  	/* Setup the timer, when timeout != NULL */

  	if (unlikely(timeout))

  		hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);

  	ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);

  
  	if (likely(!ret))

  		/* sleep on the mutex */

  		ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);

  	if (unlikely(ret)) {

  		__set_current_state(TASK_RUNNING);

  		if (rt_mutex_has_waiters(lock))
  			remove_waiter(lock, &waiter);

  		rt_mutex_handle_deadlock(ret, chwalk, &waiter);

  	}

  
  	/*
  	 * try_to_take_rt_mutex() sets the waiter bit
  	 * unconditionally. We might have to fix that up.
  	 */
  	fixup_rt_mutex_waiters(lock);

  	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

  
  	/* Remove pending timer: */
  	if (unlikely(timeout))
  		hrtimer_cancel(&timeout->timer);

  	debug_rt_mutex_free_waiter(&waiter);
  
  	return ret;
  }

  static inline int __rt_mutex_slowtrylock(struct rt_mutex *lock)
  {
  	int ret = try_to_take_rt_mutex(lock, current, NULL);
  
  	/*
  	 * try_to_take_rt_mutex() sets the lock waiters bit
  	 * unconditionally. Clean this up.
  	 */
  	fixup_rt_mutex_waiters(lock);
  
  	return ret;
  }

  /*
   * Slow path try-lock function:
   */

  static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)

  {

  	unsigned long flags;

  	int ret;
  
  	/*
  	 * If the lock already has an owner we fail to get the lock.
  	 * This can be done without taking the @lock->wait_lock as
  	 * it is only being read, and this is a trylock anyway.
  	 */
  	if (rt_mutex_owner(lock))
  		return 0;

  	/*

  	 * The mutex has currently no owner. Lock the wait lock and try to
  	 * acquire the lock. We use irqsave here to support early boot calls.

  	 */

  	raw_spin_lock_irqsave(&lock->wait_lock, flags);

  	ret = __rt_mutex_slowtrylock(lock);

  	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

  
  	return ret;
  }
  
  /*

   * Slow path to release a rt-mutex.

   *
   * Return whether the current task needs to call rt_mutex_postunlock().

   */

  static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
  					struct wake_q_head *wake_q)

  {

  	unsigned long flags;
  
  	/* irqsave required to support early boot calls */
  	raw_spin_lock_irqsave(&lock->wait_lock, flags);

  
  	debug_rt_mutex_unlock(lock);

  	/*
  	 * We must be careful here if the fast path is enabled. If we
  	 * have no waiters queued we cannot set owner to NULL here
  	 * because of:
  	 *
  	 * foo->lock->owner = NULL;
  	 *			rtmutex_lock(foo->lock);   <- fast path
  	 *			free = atomic_dec_and_test(foo->refcnt);
  	 *			rtmutex_unlock(foo->lock); <- fast path
  	 *			if (free)
  	 *				kfree(foo);
  	 * raw_spin_unlock(foo->lock->wait_lock);
  	 *
  	 * So for the fastpath enabled kernel:
  	 *
  	 * Nothing can set the waiters bit as long as we hold
  	 * lock->wait_lock. So we do the following sequence:
  	 *
  	 *	owner = rt_mutex_owner(lock);
  	 *	clear_rt_mutex_waiters(lock);
  	 *	raw_spin_unlock(&lock->wait_lock);
  	 *	if (cmpxchg(&lock->owner, owner, 0) == owner)
  	 *		return;
  	 *	goto retry;
  	 *
  	 * The fastpath disabled variant is simple as all access to
  	 * lock->owner is serialized by lock->wait_lock:
  	 *
  	 *	lock->owner = NULL;
  	 *	raw_spin_unlock(&lock->wait_lock);
  	 */
  	while (!rt_mutex_has_waiters(lock)) {
  		/* Drops lock->wait_lock ! */

  		if (unlock_rt_mutex_safe(lock, flags) == true)

  			return false;

  		/* Relock the rtmutex and try again */

  		raw_spin_lock_irqsave(&lock->wait_lock, flags);

  	}

  	/*
  	 * The wakeup next waiter path does not suffer from the above
  	 * race. See the comments there.

  	 *
  	 * Queue the next waiter for wakeup once we release the wait_lock.

  	 */

  	mark_wakeup_next_waiter(wake_q, lock);

  	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

  	return true; /* call rt_mutex_postunlock() */

  }
  
  /*
   * 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 (*slowfn)(struct rt_mutex *lock, int state,
  				struct hrtimer_sleeper *timeout,

  				enum rtmutex_chainwalk chwalk))

  {

  	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))

  		return 0;

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

  }
  
  static inline int
  rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,

  			struct hrtimer_sleeper *timeout,
  			enum rtmutex_chainwalk chwalk,

  			int (*slowfn)(struct rt_mutex *lock, int state,
  				      struct hrtimer_sleeper *timeout,

  				      enum rtmutex_chainwalk chwalk))

  {

  	if (chwalk == RT_MUTEX_MIN_CHAINWALK &&

  	    likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))

  		return 0;

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

  }
  
  static inline int
  rt_mutex_fasttrylock(struct rt_mutex *lock,

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

  {

  	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))

  		return 1;

  	return slowfn(lock);

  }

  /*

   * Performs the wakeup of the the top-waiter and re-enables preemption.

   */

  void rt_mutex_postunlock(struct wake_q_head *wake_q)

  {
  	wake_up_q(wake_q);
  
  	/* Pairs with preempt_disable() in rt_mutex_slowunlock() */

  	preempt_enable();

  }

  static inline void
  rt_mutex_fastunlock(struct rt_mutex *lock,

  		    bool (*slowfn)(struct rt_mutex *lock,
  				   struct wake_q_head *wqh))

  {

  	DEFINE_WAKE_Q(wake_q);

  	if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
  		return;

  	if (slowfn(lock, &wake_q))
  		rt_mutex_postunlock(&wake_q);

  }

  static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
  {
  	might_sleep();
  
  	mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
  	rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
  }
  
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  /**
   * rt_mutex_lock_nested - lock a rt_mutex
   *
   * @lock: the rt_mutex to be locked
   * @subclass: the lockdep subclass
   */
  void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
  {
  	__rt_mutex_lock(lock, subclass);
  }
  EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
  #endif
  
  #ifndef CONFIG_DEBUG_LOCK_ALLOC

  /**
   * rt_mutex_lock - lock a rt_mutex
   *
   * @lock: the rt_mutex to be locked
   */
  void __sched rt_mutex_lock(struct rt_mutex *lock)
  {

  	__rt_mutex_lock(lock, 0);

  }
  EXPORT_SYMBOL_GPL(rt_mutex_lock);

  #endif

  
  /**
   * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
   *

   * @lock:		the rt_mutex to be locked

   *
   * Returns:

   *  0		on success
   * -EINTR	when interrupted by a signal

   */

  int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)

  {

  	int ret;

  	might_sleep();

  	mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
  	ret = rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
  	if (ret)
  		mutex_release(&lock->dep_map, 1, _RET_IP_);
  
  	return ret;

  }
  EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);

  /*

   * Futex variant, must not use fastpath.
   */
  int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
  {
  	return rt_mutex_slowtrylock(lock);

  }

  int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
  {
  	return __rt_mutex_slowtrylock(lock);
  }

  /**

   * rt_mutex_timed_lock - 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)

   *
   * Returns:

   *  0		on success
   * -EINTR	when interrupted by a signal

   * -ETIMEDOUT	when the timeout expired

   */
  int

  rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)

  {

  	int ret;

  	might_sleep();

  	mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
  	ret = rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,

  				       RT_MUTEX_MIN_CHAINWALK,

  				       rt_mutex_slowlock);

  	if (ret)
  		mutex_release(&lock->dep_map, 1, _RET_IP_);
  
  	return ret;

  }
  EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
  
  /**
   * rt_mutex_trylock - try to lock a rt_mutex
   *
   * @lock:	the rt_mutex to be locked
   *

   * This function can only be called in thread context. It's safe to
   * call it from atomic regions, but not from hard interrupt or soft
   * interrupt context.
   *

   * Returns 1 on success and 0 on contention
   */
  int __sched rt_mutex_trylock(struct rt_mutex *lock)
  {

  	int ret;

  	if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))

  		return 0;

  	ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
  	if (ret)
  		mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
  
  	return ret;

  }
  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)
  {

  	mutex_release(&lock->dep_map, 1, _RET_IP_);

  	rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
  }
  EXPORT_SYMBOL_GPL(rt_mutex_unlock);

  /**

   * Futex variant, that since futex variants do not use the fast-path, can be
   * simple and will not need to retry.

   */

  bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
  				    struct wake_q_head *wake_q)

  {

  	lockdep_assert_held(&lock->wait_lock);
  
  	debug_rt_mutex_unlock(lock);
  
  	if (!rt_mutex_has_waiters(lock)) {
  		lock->owner = NULL;
  		return false; /* done */
  	}

  	/*

  	 * We've already deboosted, mark_wakeup_next_waiter() will
  	 * retain preempt_disabled when we drop the wait_lock, to
  	 * avoid inversion prior to the wakeup.  preempt_disable()
  	 * therein pairs with rt_mutex_postunlock().

  	 */

  	mark_wakeup_next_waiter(wake_q, lock);

  	return true; /* call postunlock() */

  }

  void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
  {
  	DEFINE_WAKE_Q(wake_q);

  	bool postunlock;

  
  	raw_spin_lock_irq(&lock->wait_lock);

  	postunlock = __rt_mutex_futex_unlock(lock, &wake_q);

  	raw_spin_unlock_irq(&lock->wait_lock);

  	if (postunlock)
  		rt_mutex_postunlock(&wake_q);

  }
  
  /**

   * 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,
  		     struct lock_class_key *key)

  {
  	lock->owner = NULL;

  	raw_spin_lock_init(&lock->wait_lock);

  	lock->waiters = RB_ROOT_CACHED;

  	if (name && key)
  		debug_rt_mutex_init(lock, name, key);

  }
  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. This initializes the rtmutex and
   * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
   * possible at this point because the pi_state which contains the rtmutex
   * is not yet visible to other tasks.

   */
  void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
  				struct task_struct *proxy_owner)
  {

  	__rt_mutex_init(lock, NULL, NULL);

  	debug_rt_mutex_proxy_lock(lock, proxy_owner);

  	rt_mutex_set_owner(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. This merrily cleans up the rtmutex
   * (debugging) state. Concurrent operations on this rt_mutex are not
   * possible because it belongs to the pi_state which is about to be freed
   * and it is not longer visible to other tasks.

   */
  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);

  }

  int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,

  			      struct rt_mutex_waiter *waiter,

  			      struct task_struct *task)

  {
  	int ret;

  	if (try_to_take_rt_mutex(lock, task, NULL))

  		return 1;

  	/* We enforce deadlock detection for futexes */

  	ret = task_blocks_on_rt_mutex(lock, waiter, task,
  				      RT_MUTEX_FULL_CHAINWALK);