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

1 files changed, 29 insertions, 3 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index ea6ca0b..c4a182f 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -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;