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

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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
parent e3d8238d7f 9f40a51a35
commit a262948335
3 changed files with 88 additions and 34 deletions
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32
kernel/futex.c
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@@ -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;