ClabureDB: Classified Bug-Reports Database

   /*
    * 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)\n", 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;
}