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rtmutex.c

/*
 * 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(&timeout->timer, timeout->timer.expires,
                        HRTIMER_MODE_ABS);

      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;
}

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