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, 56 insertions, 31 deletions

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 36573e96a477..5674b073473c 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -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);
+        }
 }
 
 /**
@@ -1467,6 +1475,23 @@ 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
  *