rt_mutex: add proxy lock routines
This patch is a prerequisite for futex requeue_pi. It basically splits rt_mutex_slowlock() right down the middle, just before the first call to schedule(). It further adds helper functions which make use of the split and provide the rt-mutex preliminaries for futex requeue_pi. Signed-off-by: Darren Hart <dvhltc@us.ibm.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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dd9739980b
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8dac456a68
288
kernel/rtmutex.c
288
kernel/rtmutex.c
@ -300,7 +300,8 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
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* assigned pending owner [which might not have taken the
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* lock yet]:
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*/
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static inline int try_to_steal_lock(struct rt_mutex *lock)
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static inline int try_to_steal_lock(struct rt_mutex *lock,
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struct task_struct *task)
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{
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struct task_struct *pendowner = rt_mutex_owner(lock);
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struct rt_mutex_waiter *next;
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@ -309,11 +310,11 @@ static inline int try_to_steal_lock(struct rt_mutex *lock)
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if (!rt_mutex_owner_pending(lock))
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return 0;
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if (pendowner == current)
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if (pendowner == task)
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return 1;
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spin_lock_irqsave(&pendowner->pi_lock, flags);
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if (current->prio >= pendowner->prio) {
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if (task->prio >= pendowner->prio) {
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spin_unlock_irqrestore(&pendowner->pi_lock, flags);
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return 0;
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}
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@ -338,21 +339,21 @@ static inline int try_to_steal_lock(struct rt_mutex *lock)
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* We are going to steal the lock and a waiter was
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* enqueued on the pending owners pi_waiters queue. So
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* we have to enqueue this waiter into
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* current->pi_waiters list. This covers the case,
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* where current is boosted because it holds another
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* task->pi_waiters list. This covers the case,
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* where task is boosted because it holds another
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* lock and gets unboosted because the booster is
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* interrupted, so we would delay a waiter with higher
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* priority as current->normal_prio.
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* priority as task->normal_prio.
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*
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* Note: in the rare case of a SCHED_OTHER task changing
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* its priority and thus stealing the lock, next->task
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* might be current:
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* might be task:
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*/
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if (likely(next->task != current)) {
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spin_lock_irqsave(¤t->pi_lock, flags);
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plist_add(&next->pi_list_entry, ¤t->pi_waiters);
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__rt_mutex_adjust_prio(current);
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spin_unlock_irqrestore(¤t->pi_lock, flags);
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if (likely(next->task != task)) {
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spin_lock_irqsave(&task->pi_lock, flags);
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plist_add(&next->pi_list_entry, &task->pi_waiters);
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__rt_mutex_adjust_prio(task);
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spin_unlock_irqrestore(&task->pi_lock, flags);
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}
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return 1;
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}
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@ -389,7 +390,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock)
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*/
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mark_rt_mutex_waiters(lock);
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if (rt_mutex_owner(lock) && !try_to_steal_lock(lock))
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if (rt_mutex_owner(lock) && !try_to_steal_lock(lock, current))
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return 0;
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/* We got the lock. */
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@ -411,6 +412,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock)
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*/
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static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
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struct rt_mutex_waiter *waiter,
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struct task_struct *task,
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int detect_deadlock)
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{
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struct task_struct *owner = rt_mutex_owner(lock);
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@ -418,21 +420,21 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
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unsigned long flags;
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int chain_walk = 0, res;
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spin_lock_irqsave(¤t->pi_lock, flags);
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__rt_mutex_adjust_prio(current);
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waiter->task = current;
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spin_lock_irqsave(&task->pi_lock, flags);
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__rt_mutex_adjust_prio(task);
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waiter->task = task;
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waiter->lock = lock;
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plist_node_init(&waiter->list_entry, current->prio);
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plist_node_init(&waiter->pi_list_entry, current->prio);
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plist_node_init(&waiter->list_entry, task->prio);
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plist_node_init(&waiter->pi_list_entry, task->prio);
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/* Get the top priority waiter on the lock */
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if (rt_mutex_has_waiters(lock))
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top_waiter = rt_mutex_top_waiter(lock);
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plist_add(&waiter->list_entry, &lock->wait_list);
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current->pi_blocked_on = waiter;
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task->pi_blocked_on = waiter;
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spin_unlock_irqrestore(¤t->pi_lock, flags);
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spin_unlock_irqrestore(&task->pi_lock, flags);
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if (waiter == rt_mutex_top_waiter(lock)) {
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spin_lock_irqsave(&owner->pi_lock, flags);
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@ -460,7 +462,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
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spin_unlock(&lock->wait_lock);
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res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
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current);
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task);
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spin_lock(&lock->wait_lock);
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@ -605,6 +607,85 @@ void rt_mutex_adjust_pi(struct task_struct *task)
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rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
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}
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/**
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* __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
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* @lock: the rt_mutex to take
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* @state: the state the task should block in (TASK_INTERRUPTIBLE
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* or TASK_UNINTERRUPTIBLE)
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* @timeout: the pre-initialized and started timer, or NULL for none
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* @waiter: the pre-initialized rt_mutex_waiter
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* @detect_deadlock: passed to task_blocks_on_rt_mutex
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*
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* lock->wait_lock must be held by the caller.
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*/
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static int __sched
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__rt_mutex_slowlock(struct rt_mutex *lock, int state,
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struct hrtimer_sleeper *timeout,
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struct rt_mutex_waiter *waiter,
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int detect_deadlock)
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{
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int ret = 0;
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for (;;) {
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/* Try to acquire the lock: */
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if (try_to_take_rt_mutex(lock))
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break;
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/*
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* TASK_INTERRUPTIBLE checks for signals and
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* timeout. Ignored otherwise.
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*/
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if (unlikely(state == TASK_INTERRUPTIBLE)) {
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/* Signal pending? */
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if (signal_pending(current))
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ret = -EINTR;
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if (timeout && !timeout->task)
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ret = -ETIMEDOUT;
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if (ret)
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break;
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}
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/*
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* waiter->task is NULL the first time we come here and
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* when we have been woken up by the previous owner
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* but the lock got stolen by a higher prio task.
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*/
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if (!waiter->task) {
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ret = task_blocks_on_rt_mutex(lock, waiter, current,
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detect_deadlock);
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/*
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* If we got woken up by the owner then start loop
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* all over without going into schedule to try
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* to get the lock now:
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*/
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if (unlikely(!waiter->task)) {
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/*
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* Reset the return value. We might
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* have returned with -EDEADLK and the
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* owner released the lock while we
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* were walking the pi chain.
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*/
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ret = 0;
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continue;
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}
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if (unlikely(ret))
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break;
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}
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spin_unlock(&lock->wait_lock);
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debug_rt_mutex_print_deadlock(waiter);
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if (waiter->task)
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schedule_rt_mutex(lock);
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spin_lock(&lock->wait_lock);
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set_current_state(state);
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}
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return ret;
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}
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/*
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* Slow path lock function:
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*/
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@ -636,62 +717,8 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
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timeout->task = NULL;
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}
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for (;;) {
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/* Try to acquire the lock: */
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if (try_to_take_rt_mutex(lock))
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break;
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/*
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* TASK_INTERRUPTIBLE checks for signals and
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* timeout. Ignored otherwise.
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*/
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if (unlikely(state == TASK_INTERRUPTIBLE)) {
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/* Signal pending? */
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if (signal_pending(current))
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ret = -EINTR;
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if (timeout && !timeout->task)
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ret = -ETIMEDOUT;
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if (ret)
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break;
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}
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/*
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* waiter.task is NULL the first time we come here and
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* when we have been woken up by the previous owner
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* but the lock got stolen by a higher prio task.
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*/
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if (!waiter.task) {
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ret = task_blocks_on_rt_mutex(lock, &waiter,
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detect_deadlock);
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/*
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* If we got woken up by the owner then start loop
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* all over without going into schedule to try
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* to get the lock now:
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*/
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if (unlikely(!waiter.task)) {
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/*
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* Reset the return value. We might
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* have returned with -EDEADLK and the
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* owner released the lock while we
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* were walking the pi chain.
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*/
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ret = 0;
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continue;
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}
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if (unlikely(ret))
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break;
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}
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spin_unlock(&lock->wait_lock);
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debug_rt_mutex_print_deadlock(&waiter);
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if (waiter.task)
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schedule_rt_mutex(lock);
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spin_lock(&lock->wait_lock);
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set_current_state(state);
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}
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ret = __rt_mutex_slowlock(lock, state, timeout, &waiter,
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detect_deadlock);
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set_current_state(TASK_RUNNING);
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@ -985,6 +1012,59 @@ void rt_mutex_proxy_unlock(struct rt_mutex *lock,
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rt_mutex_deadlock_account_unlock(proxy_owner);
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}
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/**
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* rt_mutex_start_proxy_lock() - Start lock acquisition for another task
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* @lock: the rt_mutex to take
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* @waiter: the pre-initialized rt_mutex_waiter
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* @task: the task to prepare
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* @detect_deadlock: perform deadlock detection (1) or not (0)
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*
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* Returns:
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* 0 - task blocked on lock
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* 1 - acquired the lock for task, caller should wake it up
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* <0 - error
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*
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* Special API call for FUTEX_REQUEUE_PI support.
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*/
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int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
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struct rt_mutex_waiter *waiter,
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struct task_struct *task, int detect_deadlock)
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{
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int ret;
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spin_lock(&lock->wait_lock);
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mark_rt_mutex_waiters(lock);
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if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
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/* We got the lock for task. */
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debug_rt_mutex_lock(lock);
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rt_mutex_set_owner(lock, task, 0);
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rt_mutex_deadlock_account_lock(lock, task);
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return 1;
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}
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ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
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if (ret && !waiter->task) {
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/*
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* Reset the return value. We might have
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* returned with -EDEADLK and the owner
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* released the lock while we were walking the
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* pi chain. Let the waiter sort it out.
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*/
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ret = 0;
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}
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spin_unlock(&lock->wait_lock);
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debug_rt_mutex_print_deadlock(waiter);
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return ret;
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}
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/**
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* rt_mutex_next_owner - return the next owner of the lock
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*
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@ -1004,3 +1084,57 @@ struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
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return rt_mutex_top_waiter(lock)->task;
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}
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/**
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* rt_mutex_finish_proxy_lock() - Complete lock acquisition
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* @lock: the rt_mutex we were woken on
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* @to: the timeout, null if none. hrtimer should already have
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* been started.
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* @waiter: the pre-initialized rt_mutex_waiter
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* @detect_deadlock: perform deadlock detection (1) or not (0)
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*
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* Complete the lock acquisition started our behalf by another thread.
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*
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* Returns:
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* 0 - success
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* <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
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*
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* Special API call for PI-futex requeue support
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*/
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int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
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struct hrtimer_sleeper *to,
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struct rt_mutex_waiter *waiter,
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int detect_deadlock)
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{
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int ret;
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spin_lock(&lock->wait_lock);
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set_current_state(TASK_INTERRUPTIBLE);
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ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter,
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detect_deadlock);
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set_current_state(TASK_RUNNING);
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if (unlikely(waiter->task))
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remove_waiter(lock, waiter);
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/*
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* try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
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* have to fix that up.
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*/
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fixup_rt_mutex_waiters(lock);
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spin_unlock(&lock->wait_lock);
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/*
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* Readjust priority, when we did not get the lock. We might have been
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* the pending owner and boosted. Since we did not take the lock, the
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* PI boost has to go.
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*/
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if (unlikely(ret))
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rt_mutex_adjust_prio(current);
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return ret;
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}
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@ -120,6 +120,14 @@ extern void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
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struct task_struct *proxy_owner);
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extern void rt_mutex_proxy_unlock(struct rt_mutex *lock,
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struct task_struct *proxy_owner);
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extern int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
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struct rt_mutex_waiter *waiter,
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struct task_struct *task,
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int detect_deadlock);
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extern int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
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struct hrtimer_sleeper *to,
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struct rt_mutex_waiter *waiter,
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int detect_deadlock);
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#ifdef CONFIG_DEBUG_RT_MUTEXES
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# include "rtmutex-debug.h"
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