Merge branch 'sched-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Thomas Gleixner:
 "These locking updates depend on the alreay merged sched/core branch:

   - Lockless top waiter wakeup for rtmutex (Davidlohr)

   - Reduce hash bucket lock contention for PI futexes (Sebastian)

   - Documentation update (Davidlohr)"

* 'sched-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/rtmutex: Update stale plist comments
  futex: Lower the lock contention on the HB lock during wake up
  locking/rtmutex: Implement lockless top-waiter wakeup
This commit is contained in:
Linus Torvalds 2015-06-24 14:46:01 -07:00
commit a262948335
3 changed files with 88 additions and 34 deletions

View File

@ -1117,11 +1117,14 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
q->lock_ptr = NULL;
}
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
struct futex_hash_bucket *hb)
{
struct task_struct *new_owner;
struct futex_pi_state *pi_state = this->pi_state;
u32 uninitialized_var(curval), newval;
WAKE_Q(wake_q);
bool deboost;
int ret = 0;
if (!pi_state)
@ -1173,7 +1176,19 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
raw_spin_unlock_irq(&new_owner->pi_lock);
raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
rt_mutex_unlock(&pi_state->pi_mutex);
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.
*/
spin_unlock(&hb->lock);
wake_up_q(&wake_q);
if (deboost)
rt_mutex_adjust_prio(current);
return 0;
}
@ -2410,13 +2425,23 @@ retry:
*/
match = futex_top_waiter(hb, &key);
if (match) {
ret = wake_futex_pi(uaddr, uval, match);
ret = wake_futex_pi(uaddr, uval, match, hb);
/*
* In case of success wake_futex_pi dropped the hash
* bucket lock.
*/
if (!ret)
goto out_putkey;
/*
* The atomic access to the futex value generated a
* pagefault, so retry the user-access and the wakeup:
*/
if (ret == -EFAULT)
goto pi_faulted;
/*
* wake_futex_pi has detected invalid state. Tell user
* space.
*/
goto out_unlock;
}
@ -2437,6 +2462,7 @@ retry:
out_unlock:
spin_unlock(&hb->lock);
out_putkey:
put_futex_key(&key);
return ret;

View File

@ -300,7 +300,7 @@ static void __rt_mutex_adjust_prio(struct task_struct *task)
* of task. We do not use the spin_xx_mutex() variants here as we are
* outside of the debug path.)
*/
static void rt_mutex_adjust_prio(struct task_struct *task)
void rt_mutex_adjust_prio(struct task_struct *task)
{
unsigned long flags;
@ -624,7 +624,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
*/
prerequeue_top_waiter = rt_mutex_top_waiter(lock);
/* [7] Requeue the waiter in the lock waiter list. */
/* [7] Requeue the waiter in the lock waiter tree. */
rt_mutex_dequeue(lock, waiter);
waiter->prio = task->prio;
rt_mutex_enqueue(lock, waiter);
@ -662,7 +662,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
/*
* The waiter became the new top (highest priority)
* waiter on the lock. Replace the previous top waiter
* in the owner tasks pi waiters list with this waiter
* in the owner tasks pi waiters tree with this waiter
* and adjust the priority of the owner.
*/
rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
@ -673,7 +673,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
/*
* The waiter was the top waiter on the lock, but is
* no longer the top prority waiter. Replace waiter in
* the owner tasks pi waiters list with the new top
* the owner tasks pi waiters tree with the new top
* (highest priority) waiter and adjust the priority
* of the owner.
* The new top waiter is stored in @waiter so that
@ -747,7 +747,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
*
* @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 if the
* @waiter: The waiter that is queued to the lock's wait tree if the
* callsite called task_blocked_on_lock(), otherwise NULL
*/
static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
@ -782,7 +782,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
/*
* If @waiter != NULL, @task has already enqueued the waiter
* into @lock waiter list. If @waiter == NULL then this is a
* into @lock waiter tree. If @waiter == NULL then this is a
* trylock attempt.
*/
if (waiter) {
@ -795,7 +795,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
/*
* We can acquire the lock. Remove the waiter from the
* lock waiters list.
* lock waiters tree.
*/
rt_mutex_dequeue(lock, waiter);
@ -827,7 +827,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
* No waiters. Take the lock without the
* pi_lock dance.@task->pi_blocked_on is NULL
* and we have no waiters to enqueue in @task
* pi waiters list.
* pi waiters tree.
*/
goto takeit;
}
@ -844,7 +844,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
/*
* Finish the lock acquisition. @task is the new owner. If
* other waiters exist we have to insert the highest priority
* waiter into @task->pi_waiters list.
* waiter into @task->pi_waiters tree.
*/
if (rt_mutex_has_waiters(lock))
rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
@ -955,14 +955,13 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
}
/*
* Wake up the next waiter on the lock.
*
* Remove the top waiter from the current tasks pi waiter list and
* wake it up.
* Remove the top waiter from the current tasks pi waiter tree and
* queue it up.
*
* Called with lock->wait_lock held.
*/
static void wakeup_next_waiter(struct rt_mutex *lock)
static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
struct rt_mutex *lock)
{
struct rt_mutex_waiter *waiter;
unsigned long flags;
@ -991,12 +990,7 @@ static void wakeup_next_waiter(struct rt_mutex *lock)
raw_spin_unlock_irqrestore(&current->pi_lock, flags);
/*
* It's safe to dereference waiter as it cannot go away as
* long as we hold lock->wait_lock. The waiter task needs to
* acquire it in order to dequeue the waiter.
*/
wake_up_process(waiter->task);
wake_q_add(wake_q, waiter->task);
}
/*
@ -1250,10 +1244,11 @@ static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
}
/*
* Slow path to release a rt-mutex:
* Slow path to release a rt-mutex.
* Return whether the current task needs to undo a potential priority boosting.
*/
static void __sched
rt_mutex_slowunlock(struct rt_mutex *lock)
static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
struct wake_q_head *wake_q)
{
raw_spin_lock(&lock->wait_lock);
@ -1295,7 +1290,7 @@ rt_mutex_slowunlock(struct rt_mutex *lock)
while (!rt_mutex_has_waiters(lock)) {
/* Drops lock->wait_lock ! */
if (unlock_rt_mutex_safe(lock) == true)
return;
return false;
/* Relock the rtmutex and try again */
raw_spin_lock(&lock->wait_lock);
}
@ -1303,13 +1298,15 @@ rt_mutex_slowunlock(struct rt_mutex *lock)
/*
* The wakeup next waiter path does not suffer from the above
* race. See the comments there.
*
* Queue the next waiter for wakeup once we release the wait_lock.
*/
wakeup_next_waiter(lock);
mark_wakeup_next_waiter(wake_q, lock);
raw_spin_unlock(&lock->wait_lock);
/* Undo pi boosting if necessary: */
rt_mutex_adjust_prio(current);
/* check PI boosting */
return true;
}
/*
@ -1360,12 +1357,23 @@ rt_mutex_fasttrylock(struct rt_mutex *lock,
static inline void
rt_mutex_fastunlock(struct rt_mutex *lock,
void (*slowfn)(struct rt_mutex *lock))
bool (*slowfn)(struct rt_mutex *lock,
struct wake_q_head *wqh))
{
if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
WAKE_Q(wake_q);
if (likely(rt_mutex_cmpxchg(lock, current, NULL))) {
rt_mutex_deadlock_account_unlock(current);
else
slowfn(lock);
} else {
bool deboost = slowfn(lock, &wake_q);
wake_up_q(&wake_q);
/* Undo pi boosting if necessary: */
if (deboost)
rt_mutex_adjust_prio(current);
}
}
/**
@ -1466,6 +1474,23 @@ 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.
*/
bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock,
struct wake_q_head *wqh)
{
if (likely(rt_mutex_cmpxchg(lock, current, NULL))) {
rt_mutex_deadlock_account_unlock(current);
return false;
}
return rt_mutex_slowunlock(lock, wqh);
}
/**
* rt_mutex_destroy - mark a mutex unusable
* @lock: the mutex to be destroyed

View File

@ -131,6 +131,9 @@ 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 void rt_mutex_adjust_prio(struct task_struct *task);
#ifdef CONFIG_DEBUG_RT_MUTEXES
# include "rtmutex-debug.h"