Esempio n. 1
0
/*
 * 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;
	waiter->prio = task->prio;

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

	task->pi_blocked_on = waiter;

	raw_spin_unlock_irqrestore(&task->pi_lock, flags);

	if (!owner)
		return 0;

	if (waiter == rt_mutex_top_waiter(lock)) {
		raw_spin_lock_irqsave(&owner->pi_lock, flags);
		rt_mutex_dequeue_pi(owner, top_waiter);
		rt_mutex_enqueue_pi(owner, waiter);

		__rt_mutex_adjust_prio(owner);
		if (owner->pi_blocked_on)
			chain_walk = 1;
		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;
}
Esempio n. 2
0
/*
 * 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 boost = 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) {
            boost = 1;
            /* gets dropped in rt_mutex_adjust_prio_chain()! */
            get_task_struct(owner);
        }
        spin_unlock_irqrestore(&owner->pi_lock, flags);
    }
    else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
        spin_lock_irqsave(&owner->pi_lock, flags);
        if (owner->pi_blocked_on) {
            boost = 1;
            /* gets dropped in rt_mutex_adjust_prio_chain()! */
            get_task_struct(owner);
        }
        spin_unlock_irqrestore(&owner->pi_lock, flags);
    }
    if (!boost)
        return 0;

    spin_unlock(&lock->wait_lock);

    res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
                                     current);

    spin_lock(&lock->wait_lock);

    return res;
}
Esempio n. 3
0
/*
 * 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, int savestate)
{
	struct rt_mutex_waiter *waiter;
	struct task_struct *pendowner;

	spin_lock(&current->pi_lock);

	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(&current->pi_lock);

	/*
	 * 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(&pendowner->pi_lock);

	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(&pendowner->pi_lock);

	if (savestate)
		wake_up_process_mutex(pendowner);
	else
		wake_up_process(pendowner);
}
Esempio n. 4
0
/*
 * 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,
			  unsigned long flags)
{
	int first = (waiter == rt_mutex_top_waiter(lock));
	struct task_struct *owner = rt_mutex_owner(lock);
	int chain_walk = 0;

	raw_spin_lock(&current->pi_lock);
	plist_del(&waiter->list_entry, &lock->wait_list);
	current->pi_blocked_on = NULL;
	raw_spin_unlock(&current->pi_lock);

	if (!owner) {
		BUG_ON(first);
		return;
	}

	if (first) {

		raw_spin_lock(&owner->pi_lock);

		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 (rt_mutex_real_waiter(owner->pi_blocked_on))
			chain_walk = 1;

		raw_spin_unlock(&owner->pi_lock);
	}

	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_irqrestore(&lock->wait_lock, flags);

	rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);

	raw_spin_lock_irq(&lock->wait_lock);
}
Esempio n. 5
0
/*
 * 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);
	rt_mutex_dequeue(lock, waiter);
	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);

		rt_mutex_dequeue_pi(owner, waiter);

		if (rt_mutex_has_waiters(lock)) {
			struct rt_mutex_waiter *next;

			next = rt_mutex_top_waiter(lock);
			rt_mutex_enqueue_pi(owner, next);
		}
		__rt_mutex_adjust_prio(owner);

		if (owner->pi_blocked_on)
			chain_walk = 1;

		raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
	}

	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);
}
Esempio n. 6
0
/**
 * 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;
}
Esempio n. 7
0
/*
 * 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, int savestate)
{
	struct rt_mutex_waiter *waiter;
	struct task_struct *top_task;

	waiter = rt_mutex_top_waiter(lock);
	top_task = waiter->task;

	/*
	 * 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.
	 */
	raw_spin_lock(&current->pi_lock);
	plist_del(&waiter->pi_list_entry, &current->pi_waiters);
	raw_spin_unlock(&current->pi_lock);

	rt_mutex_set_owner(lock, NULL);

	if (!savestate)
		wake_up_process(top_task);
	else
		wake_up_process_mutex(top_task);

	WARN_ON(!top_task->pi_blocked_on);
	WARN_ON(top_task->pi_blocked_on != waiter);
	WARN_ON(top_task->pi_blocked_on->lock != lock);
}
Esempio n. 8
0
/*
 * 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 boost = 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) {
            boost = 1;
            /* gets dropped in rt_mutex_adjust_prio_chain()! */
            get_task_struct(owner);
        }
        spin_unlock_irqrestore(&owner->pi_lock, flags);
    }

    WARN_ON(!plist_node_empty(&waiter->pi_list_entry));

    if (!boost)
        return;

    spin_unlock(&lock->wait_lock);

    rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);

    spin_lock(&lock->wait_lock);
}
Esempio n. 9
0
/*
 * 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;
}
Esempio n. 10
0
/*
 * 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);
}
Esempio n. 11
0
/*
 * 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;
}
Esempio n. 12
0
/*
 * 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;
}
Esempio n. 13
0
/*
 * 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;

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

	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;
}
Esempio n. 14
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/*
 * Slow path lock function spin_lock style: this variant is very
 * careful not to miss any non-lock wakeups.
 *
 * The wakeup side uses wake_up_process_mutex, which, combined with
 * the xchg code of this function is a transparent sleep/wakeup
 * mechanism nested within any existing sleep/wakeup mechanism. This
 * enables the seemless use of arbitrary (blocking) spinlocks within
 * sleep/wakeup event loops.
 */
static void  noinline __sched
rt_spin_lock_slowlock(struct rt_mutex *lock)
{
	struct rt_mutex_waiter waiter;
	unsigned long saved_state, flags;
	/* orig_owner is only set if next_waiter is set */
	struct task_struct *uninitialized_var(orig_owner);
	int next_waiter;
	int saved_lock_depth;
	int ret;

	debug_rt_mutex_init_waiter(&waiter);
	waiter.task = NULL;

	raw_spin_lock_irqsave(&lock->wait_lock, flags);
	init_lists(lock);

	if (do_try_to_take_rt_mutex(lock, current, NULL, STEAL_LATERAL)) {
		raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
		return;
	}

	BUG_ON(rt_mutex_owner(lock) == current);

	/*
	 * Here we save whatever state the task was in originally,
	 * we'll restore it at the end of the function and we'll take
	 * any intermediate wakeup into account as well, independently
	 * of the lock sleep/wakeup mechanism. When we get a real
	 * wakeup the task->state is TASK_RUNNING and we change
	 * saved_state accordingly. If we did not get a real wakeup
	 * then we return with the saved state. We need to be careful
	 * about original state TASK_INTERRUPTIBLE as well, as we
	 * could miss a wakeup_interruptible()
	 */
	saved_state = rt_set_current_blocked_state(current->state);

	/*
	 * Prevent schedule() to drop BKL, while waiting for
	 * the lock ! We restore lock_depth when we come back.
	 */
	saved_lock_depth = current->lock_depth;
	current->lock_depth = -1;

	ret = task_blocks_on_rt_mutex(lock, &waiter, current, 0, flags, 1);
	BUG_ON(ret);

	for (;;) {
		int sleep = 1;

		/* Try to acquire the lock again. */
		if (do_try_to_take_rt_mutex(lock, current, &waiter, STEAL_LATERAL))
			break;

		next_waiter = &waiter == rt_mutex_top_waiter(lock);
		if (next_waiter) {
			orig_owner = rt_mutex_owner(lock);
			if (orig_owner)
				get_task_struct(orig_owner);
		}
		raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

		debug_rt_mutex_print_deadlock(&waiter);

		if (next_waiter && orig_owner) {
			if (!adaptive_wait(&waiter, orig_owner))
				sleep = 0;
			put_task_struct(orig_owner);
		}
		if (sleep)
			schedule_rt_mutex(lock);

		raw_spin_lock_irqsave(&lock->wait_lock, flags);
		saved_state = rt_set_current_blocked_state(saved_state);
	}
	current->lock_depth = saved_lock_depth;

	rt_restore_current_state(saved_state);

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

	BUG_ON(rt_mutex_has_waiters(lock) && &waiter == rt_mutex_top_waiter(lock));
	BUG_ON(!plist_node_empty(&waiter.list_entry));

	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

	debug_rt_mutex_free_waiter(&waiter);
}
Esempio n. 15
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/*
 * 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, unsigned long flags,
				   int savestate)
{
	struct task_struct *owner = rt_mutex_owner(lock);
	struct rt_mutex_waiter *top_waiter = waiter;
	int chain_walk = 0, res;

	raw_spin_lock(&task->pi_lock);

	/*
	 * In the case of futex requeue PI, this will be a proxy
	 * lock. The task will wake unaware that it is enqueueed on
	 * this lock. Avoid blocking on two locks and corrupting
	 * pi_blocked_on via the PI_WAKEUP_INPROGRESS
	 * flag. futex_wait_requeue_pi() sets this when it wakes up
	 * before requeue (due to a signal or timeout). Do not enqueue
	 * the task if PI_WAKEUP_INPROGRESS is set.
	 */
	if (task != current && task->pi_blocked_on == PI_WAKEUP_INPROGRESS) {
		raw_spin_unlock(&task->pi_lock);
		return -EAGAIN;
	}

	BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on));

	__rt_mutex_adjust_prio(task);
	waiter->task = task;
	waiter->lock = lock;
	waiter->savestate = savestate;
	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(&task->pi_lock);

	if (!owner)
		return 0;

	if (waiter == rt_mutex_top_waiter(lock)) {
		raw_spin_lock(&owner->pi_lock);
		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 (rt_mutex_real_waiter(owner->pi_blocked_on))
			chain_walk = 1;
		raw_spin_unlock(&owner->pi_lock);
	}
	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_irqrestore(&lock->wait_lock, flags);

	res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
					 task);

	raw_spin_lock_irq(&lock->wait_lock);

	return res;
}