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futex,rt_mutex: Provide futex specific rt_mutex API

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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>
This commit is contained in:
Peter Zijlstra 2017-03-22 11:35:51 +01:00 • committed by Thomas Gleixner
parent fffa954fb5
commit 5293c2efda
3 changed files with 62 additions and 32 deletions
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55
kernel/locking/rtmutex.c
View file

@ -1488,15 +1488,23 @@ EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
/*
* Futex variant with full deadlock detection.
* Futex variants must not use the fast-path, see __rt_mutex_futex_unlock().
*/
int rt_mutex_timed_futex_lock(struct rt_mutex *lock,
int __sched rt_mutex_timed_futex_lock(struct rt_mutex *lock,
struct hrtimer_sleeper *timeout)
{
might_sleep();
return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
RT_MUTEX_FULL_CHAINWALK,
rt_mutex_slowlock);
return rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE,
timeout, RT_MUTEX_FULL_CHAINWALK);
}
/*
* Futex variant, must not use fastpath.
*/
int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
{
return rt_mutex_slowtrylock(lock);
}
/**
@ -1555,19 +1563,38 @@ void __sched rt_mutex_unlock(struct rt_mutex *lock)
EXPORT_SYMBOL_GPL(rt_mutex_unlock);
/**
* rt_mutex_futex_unlock - Futex variant of rt_mutex_unlock
* @lock: the rt_mutex to be unlocked
*
* Returns: true/false indicating whether priority adjustment is
* required or not.
* Futex variant, that since futex variants do not use the fast-path, can be
* simple and will not need to retry.
*/
bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock,
struct wake_q_head *wqh)
bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
struct wake_q_head *wake_q)
{
if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
return false;
lockdep_assert_held(&lock->wait_lock);
return rt_mutex_slowunlock(lock, wqh);
debug_rt_mutex_unlock(lock);
if (!rt_mutex_has_waiters(lock)) {
lock->owner = NULL;
return false; /* done */
}
mark_wakeup_next_waiter(wake_q, lock);
return true; /* deboost and wakeups */
}
void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
{
DEFINE_WAKE_Q(wake_q);
bool deboost;
raw_spin_lock_irq(&lock->wait_lock);
deboost = __rt_mutex_futex_unlock(lock, &wake_q);
raw_spin_unlock_irq(&lock->wait_lock);
if (deboost) {
wake_up_q(&wake_q);
rt_mutex_adjust_prio(current);
}
}
/**