FreeBSD/Linux Kernel Cross Reference
sys/kernel/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/export.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
     * 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)
    {
            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;
   
           raw_spin_lock_irqsave(&task->pi_lock, flags);
           __rt_mutex_adjust_prio(task);
           raw_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 !
            */
           raw_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)
                   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;
   
           /*
            * 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 (!raw_spin_trylock(&lock->wait_lock)) {
                   raw_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);
                   raw_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 */
           raw_spin_unlock_irqrestore(&task->pi_lock, flags);
           if (!rt_mutex_owner(lock)) {
                   /*
                    * If the requeue above changed the top waiter, then we need
                    * to wake the new top waiter up to try to get the lock.
                    */
   
                   if (top_waiter != rt_mutex_top_waiter(lock))
                           wake_up_process(rt_mutex_top_waiter(lock)->task);
                   raw_spin_unlock(&lock->wait_lock);
                   goto out_put_task;
           }
           put_task_struct(task);
   
           /* Grab the next task */
           task = rt_mutex_owner(lock);
           get_task_struct(task);
           raw_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);
           }
   
           raw_spin_unlock_irqrestore(&task->pi_lock, flags);
   
           top_waiter = rt_mutex_top_waiter(lock);
           raw_spin_unlock(&lock->wait_lock);
   
           if (!detect_deadlock && waiter != top_waiter)
                   goto out_put_task;
   
           goto again;
   
    out_unlock_pi:
           raw_spin_unlock_irqrestore(&task->pi_lock, flags);
    out_put_task:
           put_task_struct(task);
   
           return ret;
   }
   
   /*
    * Try to take an rt-mutex
    *
    * Must be called with lock->wait_lock held.
    *
    * @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 list. (could be NULL)
    */
   static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
                   struct rt_mutex_waiter *waiter)
   {
           /*
            * 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))
                   return 0;
   
           /*
            * It will get the lock because of one of these conditions:
            * 1) there is no waiter
            * 2) higher priority than waiters
            * 3) it is top waiter
            */
           if (rt_mutex_has_waiters(lock)) {
                   if (task->prio >= rt_mutex_top_waiter(lock)->list_entry.prio) {
                           if (!waiter || waiter != rt_mutex_top_waiter(lock))
                                   return 0;
                   }
           }
   
           if (waiter || rt_mutex_has_waiters(lock)) {
                   unsigned long flags;
                   struct rt_mutex_waiter *top;
   
                   raw_spin_lock_irqsave(&task->pi_lock, flags);
   
                   /* remove the queued waiter. */
                   if (waiter) {
                           plist_del(&waiter->list_entry, &lock->wait_list);
                           task->pi_blocked_on = NULL;
                   }
   
                   /*
                    * We have to enqueue the top waiter(if it exists) into
                    * task->pi_waiters list.
                    */
                   if (rt_mutex_has_waiters(lock)) {
                           top = rt_mutex_top_waiter(lock);
                           top->pi_list_entry.prio = top->list_entry.prio;
                           plist_add(&top->pi_list_entry, &task->pi_waiters);
                   }
                   raw_spin_unlock_irqrestore(&task->pi_lock, flags);
           }
   
           /* We got the lock. */
           debug_rt_mutex_lock(lock);
   
           rt_mutex_set_owner(lock, task);
   
           rt_mutex_deadlock_account_lock(lock, task);
   
           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,
                                      struct task_struct *task,
                                      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;
   
           raw_spin_lock_irqsave(&task->pi_lock, flags);
           __rt_mutex_adjust_prio(task);
           waiter->task = task;
           waiter->lock = lock;
           plist_node_init(&waiter->list_entry, task->prio);
           plist_node_init(&waiter->pi_list_entry, task->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);
   
           task->pi_blocked_on = waiter;
   
           raw_spin_unlock_irqrestore(&task->pi_lock, flags);
   
           if (!owner)
                   return 0;
   
           if (waiter == rt_mutex_top_waiter(lock)) {
                   raw_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;
                   raw_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);
   
           raw_spin_unlock(&lock->wait_lock);
   
           res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
                                            task);
   
           raw_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 wake it up.
    *
    * Called with lock->wait_lock held.
    */
   static void wakeup_next_waiter(struct rt_mutex *lock)
   {
           struct rt_mutex_waiter *waiter;
           unsigned long flags;
   
           raw_spin_lock_irqsave(&current->pi_lock, flags);
   
           waiter = rt_mutex_top_waiter(lock);
   
           /*
            * 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);
   
           rt_mutex_set_owner(lock, NULL);
   
           raw_spin_unlock_irqrestore(&current->pi_lock, flags);
   
           wake_up_process(waiter->task);
   }
   
   /*
    * Remove a waiter from a lock and give up
    *
    * Must be called with lock->wait_lock held and
    * have just failed to try_to_take_rt_mutex().
    */
   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;
   
           raw_spin_lock_irqsave(&current->pi_lock, flags);
           plist_del(&waiter->list_entry, &lock->wait_list);
           current->pi_blocked_on = NULL;
           raw_spin_unlock_irqrestore(&current->pi_lock, flags);
   
           if (!owner)
                   return;
   
           if (first) {
   
                   raw_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;
   
                   raw_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);
   
           raw_spin_unlock(&lock->wait_lock);
   
           rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
   
           raw_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;
   
           raw_spin_lock_irqsave(&task->pi_lock, flags);
   
           waiter = task->pi_blocked_on;
           if (!waiter || waiter->list_entry.prio == task->prio) {
                   raw_spin_unlock_irqrestore(&task->pi_lock, flags);
                   return;
           }
   
           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, 0, NULL, NULL, task);
   }
   
   /**
    * __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
    *
    * lock->wait_lock must be held by the caller.
    */
   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 (unlikely(state == TASK_INTERRUPTIBLE)) {
                           /* Signal pending? */
                           if (signal_pending(current))
                                   ret = -EINTR;
                           if (timeout && !timeout->task)
                                   ret = -ETIMEDOUT;
                           if (ret)
                                   break;
                   }
   
                   raw_spin_unlock(&lock->wait_lock);
   
                   debug_rt_mutex_print_deadlock(waiter);
   
                   schedule_rt_mutex(lock);
   
                   raw_spin_lock(&lock->wait_lock);
                   set_current_state(state);
           }
   
           return ret;
   }
   
   /*
    * 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);
   
           raw_spin_lock(&lock->wait_lock);
   
           /* Try to acquire the lock again: */
           if (try_to_take_rt_mutex(lock, current, NULL)) {
                   raw_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;
           }
   
           ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
   
           if (likely(!ret))
                   ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
   
           set_current_state(TASK_RUNNING);
   
           if (unlikely(ret))
                   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);
   
           raw_spin_unlock(&lock->wait_lock);
   
           /* Remove pending timer: */
           if (unlikely(timeout))
                   hrtimer_cancel(&timeout->timer);
   
           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;
   
           raw_spin_lock(&lock->wait_lock);
   
           if (likely(rt_mutex_owner(lock) != current)) {
   
                   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);
           }
   
           raw_spin_unlock(&lock->wait_lock);
   
           return ret;
   }
   
   /*
    * Slow path to release a rt-mutex:
    */
   static void __sched
   rt_mutex_slowunlock(struct rt_mutex *lock)
   {
           raw_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;
                   raw_spin_unlock(&lock->wait_lock);
                   return;
           }
   
           wakeup_next_waiter(lock);
   
           raw_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_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)
    * @detect_deadlock:    deadlock detection on/off
    *
    * Returns:
    *  0           on success
    * -EINTR       when interrupted by a signal
    * -ETIMEDOUT   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;
           raw_spin_lock_init(&lock->wait_lock);
           plist_head_init(&lock->wait_list);
   
           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);
           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);
           rt_mutex_deadlock_account_unlock(proxy_owner);
   }
   
   /**
    * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
    * @lock:               the rt_mutex to take
    * @waiter:             the pre-initialized rt_mutex_waiter
    * @task:               the task to prepare
    * @detect_deadlock:    perform deadlock detection (1) or not (0)
    *
    * Returns:
    *  0 - task blocked on lock
    *  1 - acquired the lock for task, caller should wake it up
    * <0 - error
    *
    * Special API call for FUTEX_REQUEUE_PI support.
    */
   int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
                                 struct rt_mutex_waiter *waiter,
                                 struct task_struct *task, int detect_deadlock)
   {
           int ret;
   
           raw_spin_lock(&lock->wait_lock);
   
           if (try_to_take_rt_mutex(lock, task, NULL)) {
                   raw_spin_unlock(&lock->wait_lock);
                   return 1;
           }
   
           ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
   
           if (ret && !rt_mutex_owner(lock)) {
                   /*
                    * Reset the return value. We might have
                    * returned with -EDEADLK and the owner
                    * released the lock while we were walking the
                    * pi chain.  Let the waiter sort it out.
                    */
                   ret = 0;
           }
   
           if (unlikely(ret))
                   remove_waiter(lock, waiter);
   
           raw_spin_unlock(&lock->wait_lock);
   
           debug_rt_mutex_print_deadlock(waiter);
   
           return ret;
   }
   
   /**
    * 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;
  }
  
  /**
   * rt_mutex_finish_proxy_lock() - Complete lock acquisition
   * @lock:               the rt_mutex we were woken on
   * @to:                 the timeout, null if none. hrtimer should already have
   *                      been started.
   * @waiter:             the pre-initialized rt_mutex_waiter
   * @detect_deadlock:    perform deadlock detection (1) or not (0)
   *
   * Complete the lock acquisition started our behalf by another thread.
   *
   * Returns:
   *  0 - success
   * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
   *
   * Special API call for PI-futex requeue support
   */
  int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
                                 struct hrtimer_sleeper *to,
                                 struct rt_mutex_waiter *waiter,
                                 int detect_deadlock)
  {
          int ret;
  
          raw_spin_lock(&lock->wait_lock);
  
          set_current_state(TASK_INTERRUPTIBLE);
  
          ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
  
          set_current_state(TASK_RUNNING);
  
          if (unlikely(ret))
                  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);
  
          raw_spin_unlock(&lock->wait_lock);
  
          return ret;
  }

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