futex,rt_mutex: Provide futex specific rt_mutex API
Part of what makes futex_unlock_pi() intricate is that rt_mutex_futex_unlock() -> rt_mutex_slowunlock() can drop rt_mutex::wait_lock. This means it cannot rely on the atomicy of wait_lock, which would be preferred in order to not rely on hb->lock so much. The reason rt_mutex_slowunlock() needs to drop wait_lock is because it can race with the rt_mutex fastpath, however futexes have their own fast path. Since futexes already have a bunch of separate rt_mutex accessors, complete that set and implement a rt_mutex variant without fastpath for them. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: juri.lelli@arm.com Cc: bigeasy@linutronix.de Cc: xlpang@redhat.com Cc: rostedt@goodmis.org Cc: mathieu.desnoyers@efficios.com Cc: jdesfossez@efficios.com Cc: dvhart@infradead.org Cc: bristot@redhat.com Link: http://lkml.kernel.org/r/20170322104151.702962446@infradead.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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@ -916,7 +916,7 @@ void exit_pi_state_list(struct task_struct *curr)
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pi_state->owner = NULL;
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raw_spin_unlock_irq(&curr->pi_lock);
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rt_mutex_unlock(&pi_state->pi_mutex);
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rt_mutex_futex_unlock(&pi_state->pi_mutex);
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spin_unlock(&hb->lock);
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@ -1364,20 +1364,18 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *top_waiter
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pi_state->owner = new_owner;
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raw_spin_unlock(&new_owner->pi_lock);
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raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
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deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
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/*
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* First unlock HB so the waiter does not spin on it once he got woken
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* up. Second wake up the waiter before the priority is adjusted. If we
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* deboost first (and lose our higher priority), then the task might get
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* scheduled away before the wake up can take place.
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* We've updated the uservalue, this unlock cannot fail.
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*/
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deboost = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
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raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
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spin_unlock(&hb->lock);
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wake_up_q(&wake_q);
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if (deboost)
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if (deboost) {
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wake_up_q(&wake_q);
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rt_mutex_adjust_prio(current);
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}
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return 0;
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}
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@ -2253,7 +2251,7 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
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* task acquired the rt_mutex after we removed ourself from the
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* rt_mutex waiters list.
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*/
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if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
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if (rt_mutex_futex_trylock(&q->pi_state->pi_mutex)) {
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locked = 1;
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goto out;
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}
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@ -2568,7 +2566,7 @@ retry_private:
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if (!trylock) {
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ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to);
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} else {
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ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
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ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
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/* Fixup the trylock return value: */
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ret = ret ? 0 : -EWOULDBLOCK;
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}
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@ -2591,7 +2589,7 @@ retry_private:
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* it and return the fault to userspace.
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*/
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if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
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rt_mutex_unlock(&q.pi_state->pi_mutex);
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rt_mutex_futex_unlock(&q.pi_state->pi_mutex);
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/* Unqueue and drop the lock */
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unqueue_me_pi(&q);
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@ -2898,7 +2896,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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spin_lock(q.lock_ptr);
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ret = fixup_pi_state_owner(uaddr2, &q, current);
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if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current)
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rt_mutex_unlock(&q.pi_state->pi_mutex);
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rt_mutex_futex_unlock(&q.pi_state->pi_mutex);
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/*
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* Drop the reference to the pi state which
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* the requeue_pi() code acquired for us.
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@ -2938,7 +2936,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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* userspace.
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*/
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if (ret && rt_mutex_owner(pi_mutex) == current)
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rt_mutex_unlock(pi_mutex);
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rt_mutex_futex_unlock(pi_mutex);
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/* Unqueue and drop the lock. */
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unqueue_me_pi(&q);
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@ -1488,15 +1488,23 @@ EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
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/*
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* Futex variant with full deadlock detection.
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* Futex variants must not use the fast-path, see __rt_mutex_futex_unlock().
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*/
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int rt_mutex_timed_futex_lock(struct rt_mutex *lock,
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int __sched rt_mutex_timed_futex_lock(struct rt_mutex *lock,
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struct hrtimer_sleeper *timeout)
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{
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might_sleep();
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return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
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RT_MUTEX_FULL_CHAINWALK,
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rt_mutex_slowlock);
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return rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE,
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timeout, RT_MUTEX_FULL_CHAINWALK);
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}
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/*
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* Futex variant, must not use fastpath.
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*/
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int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
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{
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return rt_mutex_slowtrylock(lock);
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}
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/**
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@ -1555,19 +1563,38 @@ void __sched rt_mutex_unlock(struct rt_mutex *lock)
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EXPORT_SYMBOL_GPL(rt_mutex_unlock);
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/**
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* rt_mutex_futex_unlock - Futex variant of rt_mutex_unlock
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* @lock: the rt_mutex to be unlocked
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*
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* Returns: true/false indicating whether priority adjustment is
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* required or not.
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* Futex variant, that since futex variants do not use the fast-path, can be
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* simple and will not need to retry.
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*/
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bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock,
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struct wake_q_head *wqh)
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bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
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struct wake_q_head *wake_q)
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{
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if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
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return false;
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lockdep_assert_held(&lock->wait_lock);
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return rt_mutex_slowunlock(lock, wqh);
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debug_rt_mutex_unlock(lock);
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if (!rt_mutex_has_waiters(lock)) {
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lock->owner = NULL;
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return false; /* done */
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}
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mark_wakeup_next_waiter(wake_q, lock);
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return true; /* deboost and wakeups */
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}
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void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
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{
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DEFINE_WAKE_Q(wake_q);
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bool deboost;
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raw_spin_lock_irq(&lock->wait_lock);
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deboost = __rt_mutex_futex_unlock(lock, &wake_q);
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raw_spin_unlock_irq(&lock->wait_lock);
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if (deboost) {
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wake_up_q(&wake_q);
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rt_mutex_adjust_prio(current);
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}
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}
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/**
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@ -109,9 +109,14 @@ extern int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
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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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extern int rt_mutex_timed_futex_lock(struct rt_mutex *l, struct hrtimer_sleeper *to);
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extern bool rt_mutex_futex_unlock(struct rt_mutex *lock,
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struct wake_q_head *wqh);
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extern int rt_mutex_futex_trylock(struct rt_mutex *l);
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extern void rt_mutex_futex_unlock(struct rt_mutex *lock);
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extern bool __rt_mutex_futex_unlock(struct rt_mutex *lock,
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struct wake_q_head *wqh);
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extern void rt_mutex_adjust_prio(struct task_struct *task);
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#ifdef CONFIG_DEBUG_RT_MUTEXES
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