signals: annotate lock context change on ptrace_stop()

[mirror_ubuntu-artful-kernel.git] / 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/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;

        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 || !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 (!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);
        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;
}

/*
 * 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 *task)
{
        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 == task)
                return 1;

        raw_spin_lock_irqsave(&pendowner->pi_lock, flags);
        if (task->prio >= pendowner->prio) {
                raw_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))) {
                raw_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);
        raw_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
         * task->pi_waiters list. This covers the case,
         * where task 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 task->normal_prio.
         *
         * Note: in the rare case of a SCHED_OTHER task changing
         * its priority and thus stealing the lock, next->task
         * might be task:
         */
        if (likely(next->task != task)) {
                raw_spin_lock_irqsave(&task->pi_lock, flags);
                plist_add(&next->pi_list_entry, &task->pi_waiters);
                __rt_mutex_adjust_prio(task);
                raw_spin_unlock_irqrestore(&task->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, current))
                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,
                                   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 (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 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;

        raw_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);

        raw_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.
         */
        raw_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);
        }
        raw_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;

        raw_spin_lock_irqsave(&current->pi_lock, flags);
        plist_del(&waiter->list_entry, &lock->wait_list);
        waiter->task = NULL;
        current->pi_blocked_on = NULL;
        raw_spin_unlock_irqrestore(&current->pi_lock, flags);

        if (first && owner != current) {

                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
 * @detect_deadlock:     passed to task_blocks_on_rt_mutex
 *
 * 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 detect_deadlock)
{
        int ret = 0;

        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, current,
                                                      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;
                }

                raw_spin_unlock(&lock->wait_lock);

                debug_rt_mutex_print_deadlock(waiter);

                if (waiter->task)
                        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);
        waiter.task = NULL;

        raw_spin_lock(&lock->wait_lock);

        /* Try to acquire the lock again: */
        if (try_to_take_rt_mutex(lock)) {
                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 = __rt_mutex_slowlock(lock, state, timeout, &waiter,
                                  detect_deadlock);

        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);

        raw_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;

        raw_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);
        }

        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_raw(&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_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);

        mark_rt_mutex_waiters(lock);

        if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
                /* We got the lock for task. */
                debug_rt_mutex_lock(lock);
                rt_mutex_set_owner(lock, task, 0);
                raw_spin_unlock(&lock->wait_lock);
                rt_mutex_deadlock_account_lock(lock, task);
                return 1;
        }

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

        if (ret && !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.  Let the waiter sort it out.
                 */
                ret = 0;
        }
        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,
                                  detect_deadlock);

        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);

        raw_spin_unlock(&lock->wait_lock);

        /*
         * 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);

        return ret;
}