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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>
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
kernel/futex.c
View File

@ -916,7 +916,7 @@ void exit_pi_state_list(struct task_struct *curr)
pi_state->owner = NULL;
raw_spin_unlock_irq(&curr->pi_lock);
rt_mutex_unlock(&pi_state->pi_mutex);
rt_mutex_futex_unlock(&pi_state->pi_mutex);
spin_unlock(&hb->lock);
@ -1364,20 +1364,18 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *top_waiter
pi_state->owner = new_owner;
raw_spin_unlock(&new_owner->pi_lock);
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
/*
* First unlock HB so the waiter does not spin on it once he got woken
* up. Second wake up the waiter before the priority is adjusted. If we
* deboost first (and lose our higher priority), then the task might get
* scheduled away before the wake up can take place.
* We've updated the uservalue, this unlock cannot fail.
*/
deboost = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
spin_unlock(&hb->lock);
wake_up_q(&wake_q);
if (deboost)
if (deboost) {
wake_up_q(&wake_q);
rt_mutex_adjust_prio(current);
}
return 0;
}
@ -2253,7 +2251,7 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
* task acquired the rt_mutex after we removed ourself from the
* rt_mutex waiters list.
*/
if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
if (rt_mutex_futex_trylock(&q->pi_state->pi_mutex)) {
locked = 1;
goto out;
}
@ -2568,7 +2566,7 @@ retry_private:
if (!trylock) {
ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to);
} else {
ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
/* Fixup the trylock return value: */
ret = ret ? 0 : -EWOULDBLOCK;
}
@ -2591,7 +2589,7 @@ retry_private:
* it and return the fault to userspace.
*/
if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
rt_mutex_unlock(&q.pi_state->pi_mutex);
rt_mutex_futex_unlock(&q.pi_state->pi_mutex);
/* Unqueue and drop the lock */
unqueue_me_pi(&q);
@ -2898,7 +2896,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
spin_lock(q.lock_ptr);
ret = fixup_pi_state_owner(uaddr2, &q, current);
if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current)
rt_mutex_unlock(&q.pi_state->pi_mutex);
rt_mutex_futex_unlock(&q.pi_state->pi_mutex);
/*
* Drop the reference to the pi state which
* the requeue_pi() code acquired for us.
@ -2938,7 +2936,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
* userspace.
*/
if (ret && rt_mutex_owner(pi_mutex) == current)
rt_mutex_unlock(pi_mutex);
rt_mutex_futex_unlock(pi_mutex);
/* Unqueue and drop the lock. */
unqueue_me_pi(&q);

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);
}
}
/**

9
kernel/locking/rtmutex_common.h
View File

@ -109,9 +109,14 @@ extern int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
extern int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
struct hrtimer_sleeper *to,
struct rt_mutex_waiter *waiter);
extern int rt_mutex_timed_futex_lock(struct rt_mutex *l, struct hrtimer_sleeper *to);
extern bool rt_mutex_futex_unlock(struct rt_mutex *lock,
struct wake_q_head *wqh);
extern int rt_mutex_futex_trylock(struct rt_mutex *l);
extern void rt_mutex_futex_unlock(struct rt_mutex *lock);
extern bool __rt_mutex_futex_unlock(struct rt_mutex *lock,
struct wake_q_head *wqh);
extern void rt_mutex_adjust_prio(struct task_struct *task);
#ifdef CONFIG_DEBUG_RT_MUTEXES