1 files changed, 113 insertions, 205 deletions

diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index a9604815786..ab449117aaf 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -20,41 +20,34 @@
 /*
  * lock->owner state tracking:
  *
- * lock->owner holds the task_struct pointer of the owner. Bit 0 and 1
- * are used to keep track of the "owner is pending" and "lock has
- * waiters" state.
+ * lock->owner holds the task_struct pointer of the owner. Bit 0
+ * is used to keep track of the "lock has waiters" state.
  *
- * owner        bit1    bit0
- * NULL         0       0       lock is free (fast acquire possible)
- * NULL         0       1       invalid state
- * NULL         1       0       Transitional State*
- * NULL         1       1       invalid state
- * taskpointer  0       0       lock is held (fast release possible)
- * taskpointer  0       1       task is pending owner
- * taskpointer  1       0       lock is held and has waiters
- * taskpointer  1       1       task is pending owner and lock has more waiters
- *
- * Pending ownership is assigned to the top (highest priority)
- * waiter of the lock, when the lock is released. The thread is woken
- * up and can now take the lock. Until the lock is taken (bit 0
- * cleared) a competing higher priority thread can steal the lock
- * which puts the woken up thread back on the waiters list.
+ * owner        bit0
+ * NULL         0       lock is free (fast acquire possible)
+ * NULL         1       lock is free and has waiters and the top waiter
+ *                              is going to take the lock*
+ * taskpointer  0       lock is held (fast release possible)
+ * taskpointer  1       lock is held and has waiters**
  *
  * The fast atomic compare exchange based acquire and release is only
- * possible when bit 0 and 1 of lock->owner are 0.
+ * possible when bit 0 of lock->owner is 0.
+ *
+ * (*) It also can be a transitional state when grabbing the lock
+ * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
+ * we need to set the bit0 before looking at the lock, and the owner may be
+ * NULL in this small time, hence this can be a transitional state.
  *
- * (*) There's a small time where the owner can be NULL and the
- * "lock has waiters" bit is set.  This can happen when grabbing the lock.
- * To prevent a cmpxchg of the owner releasing the lock, we need to set this
- * bit before looking at the lock, hence the reason this is a transitional
- * state.
+ * (**) There is a small time when bit 0 is set but there are no
+ * waiters. This can happen when grabbing the lock in the slow path.
+ * To prevent a cmpxchg of the owner releasing the lock, we need to
+ * set this bit before looking at the lock.
  */
 
 static void
-rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner,
-                   unsigned long mask)
+rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
 {
-        unsigned long val = (unsigned long)owner | mask;
+        unsigned long val = (unsigned long)owner;
 
         if (rt_mutex_has_waiters(lock))
                 val |= RT_MUTEX_HAS_WAITERS;
@@ -203,15 +196,14 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
          * reached or the state of the chain has changed while we
          * dropped the locks.
          */
-        if (!waiter || !waiter->task)
+        if (!waiter)
                 goto out_unlock_pi;
 
         /*
          * Check the orig_waiter state. After we dropped the locks,
-         * the previous owner of the lock might have released the lock
-         * and made us the pending owner:
+         * the previous owner of the lock might have released the lock.
          */
-        if (orig_waiter && !orig_waiter->task)
+        if (orig_waiter && !rt_mutex_owner(orig_lock))
                 goto out_unlock_pi;
 
         /*
@@ -254,6 +246,17 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 
         /* Release the task */
         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+        if (!rt_mutex_owner(lock)) {
+                /*
+                 * If the requeue above changed the top waiter, then we need
+                 * to wake the new top waiter up to try to get the lock.
+                 */
+
+                if (top_waiter != rt_mutex_top_waiter(lock))
+                        wake_up_process(rt_mutex_top_waiter(lock)->task);
+                raw_spin_unlock(&lock->wait_lock);
+                goto out_put_task;
+        }
         put_task_struct(task);
 
         /* Grab the next task */
@@ -296,78 +299,16 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 }
 
 /*
- * Optimization: check if we can steal the lock from the
- * assigned pending owner [which might not have taken the
- * lock yet]:
- */
-static inline int try_to_steal_lock(struct rt_mutex *lock,
-                                    struct task_struct *task)
-{
-        struct task_struct *pendowner = rt_mutex_owner(lock);
-        struct rt_mutex_waiter *next;
-        unsigned long flags;
-
-        if (!rt_mutex_owner_pending(lock))
-                return 0;
-
-        if (pendowner == task)
-                return 1;
-
-        raw_spin_lock_irqsave(&pendowner->pi_lock, flags);
-        if (task->prio >= pendowner->prio) {
-                raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
-                return 0;
-        }
-
-        /*
-         * Check if a waiter is enqueued on the pending owners
-         * pi_waiters list. Remove it and readjust pending owners
-         * priority.
-         */
-        if (likely(!rt_mutex_has_waiters(lock))) {
-                raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
-                return 1;
-        }
-
-        /* No chain handling, pending owner is not blocked on anything: */
-        next = rt_mutex_top_waiter(lock);
-        plist_del(&next->pi_list_entry, &pendowner->pi_waiters);
-        __rt_mutex_adjust_prio(pendowner);
-        raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
-
-        /*
-         * We are going to steal the lock and a waiter was
-         * enqueued on the pending owners pi_waiters queue. So
-         * we have to enqueue this waiter into
-         * task->pi_waiters list. This covers the case,
-         * where task is boosted because it holds another
-         * lock and gets unboosted because the booster is
-         * interrupted, so we would delay a waiter with higher
-         * priority as task->normal_prio.
-         *
-         * Note: in the rare case of a SCHED_OTHER task changing
-         * its priority and thus stealing the lock, next->task
-         * might be task:
-         */
-        if (likely(next->task != task)) {
-                raw_spin_lock_irqsave(&task->pi_lock, flags);
-                plist_add(&next->pi_list_entry, &task->pi_waiters);
-                __rt_mutex_adjust_prio(task);
-                raw_spin_unlock_irqrestore(&task->pi_lock, flags);
-        }
-        return 1;
-}
-
-/*
  * Try to take an rt-mutex
  *
- * This fails
- * - when the lock has a real owner
- * - when a different pending owner exists and has higher priority than current
- *
  * Must be called with lock->wait_lock held.
+ *
+ * @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. (could be NULL)
  */
-static int try_to_take_rt_mutex(struct rt_mutex *lock)
+static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
+                struct rt_mutex_waiter *waiter)
 {
         /*
          * We have to be careful here if the atomic speedups are
@@ -390,15 +331,52 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock)
          */
         mark_rt_mutex_waiters(lock);
 
-        if (rt_mutex_owner(lock) && !try_to_steal_lock(lock, current))
+        if (rt_mutex_owner(lock))
                 return 0;
 
+        /*
+         * It will get the lock because of one of these conditions:
+         * 1) there is no waiter
+         * 2) higher priority than waiters
+         * 3) it is top waiter
+         */
+        if (rt_mutex_has_waiters(lock)) {
+                if (task->prio >= rt_mutex_top_waiter(lock)->list_entry.prio) {
+                        if (!waiter || waiter != rt_mutex_top_waiter(lock))
+                                return 0;
+                }
+        }
+
+        if (waiter || rt_mutex_has_waiters(lock)) {
+                unsigned long flags;
+                struct rt_mutex_waiter *top;
+
+                raw_spin_lock_irqsave(&task->pi_lock, flags);
+
+                /* remove the queued waiter. */
+                if (waiter) {
+                        plist_del(&waiter->list_entry, &lock->wait_list);
+                        task->pi_blocked_on = NULL;
+                }
+
+                /*
+                 * We have to enqueue the top waiter(if it exists) into
+                 * task->pi_waiters list.
+                 */
+                if (rt_mutex_has_waiters(lock)) {
+                        top = rt_mutex_top_waiter(lock);
+                        top->pi_list_entry.prio = top->list_entry.prio;
+                        plist_add(&top->pi_list_entry, &task->pi_waiters);
+                }
+                raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+        }
+
         /* We got the lock. */
         debug_rt_mutex_lock(lock);
 
-        rt_mutex_set_owner(lock, current, 0);
+        rt_mutex_set_owner(lock, task);
 
-        rt_mutex_deadlock_account_lock(lock, current);
+        rt_mutex_deadlock_account_lock(lock, task);
 
         return 1;
 }
@@ -436,6 +414,9 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 
         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 
+        if (!owner)
+                return 0;
+
         if (waiter == rt_mutex_top_waiter(lock)) {
                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
                 plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
@@ -472,21 +453,18 @@ 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 waiter list and from
- * the lock waiter list. Set it as pending owner. Then wake it up.
+ * Remove the top waiter from the current tasks waiter list and wake it up.
  *
  * Called with lock->wait_lock held.
  */
 static void wakeup_next_waiter(struct rt_mutex *lock)
 {
         struct rt_mutex_waiter *waiter;
-        struct task_struct *pendowner;
         unsigned long flags;
 
         raw_spin_lock_irqsave(&current->pi_lock, flags);
 
         waiter = rt_mutex_top_waiter(lock);
-        plist_del(&waiter->list_entry, &lock->wait_list);
 
         /*
          * Remove it from current->pi_waiters. We do not adjust a
@@ -495,43 +473,19 @@ static void wakeup_next_waiter(struct rt_mutex *lock)
          * lock->wait_lock.
          */
         plist_del(&waiter->pi_list_entry, &current->pi_waiters);
-        pendowner = waiter->task;
-        waiter->task = NULL;
 
-        rt_mutex_set_owner(lock, pendowner, RT_MUTEX_OWNER_PENDING);
+        rt_mutex_set_owner(lock, NULL);
 
         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 
-        /*
-         * Clear the pi_blocked_on variable and enqueue a possible
-         * waiter into the pi_waiters list of the pending owner. This
-         * prevents that in case the pending owner gets unboosted a
-         * waiter with higher priority than pending-owner->normal_prio
-         * is blocked on the unboosted (pending) owner.
-         */
-        raw_spin_lock_irqsave(&pendowner->pi_lock, flags);
-
-        WARN_ON(!pendowner->pi_blocked_on);
-        WARN_ON(pendowner->pi_blocked_on != waiter);
-        WARN_ON(pendowner->pi_blocked_on->lock != lock);
-
-        pendowner->pi_blocked_on = NULL;
-
-        if (rt_mutex_has_waiters(lock)) {
-                struct rt_mutex_waiter *next;
-
-                next = rt_mutex_top_waiter(lock);
-                plist_add(&next->pi_list_entry, &pendowner->pi_waiters);
-        }
-        raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
-
-        wake_up_process(pendowner);
+        wake_up_process(waiter->task);
 }
 
 /*
- * Remove a waiter from a lock
+ * Remove a waiter from a lock and give up
  *
- * Must be called with lock->wait_lock held
+ * Must be called with lock->wait_lock held and
+ * have just failed to try_to_take_rt_mutex().
  */
 static void remove_waiter(struct rt_mutex *lock,
                           struct rt_mutex_waiter *waiter)
@@ -543,11 +497,13 @@ static void remove_waiter(struct rt_mutex *lock,
 
         raw_spin_lock_irqsave(&current->pi_lock, flags);
         plist_del(&waiter->list_entry, &lock->wait_list);
-        waiter->task = NULL;
         current->pi_blocked_on = NULL;
         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 
-        if (first && owner != current) {
+        if (!owner)
+                return;
+
+        if (first) {
 
                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
 
@@ -614,21 +570,19 @@ void rt_mutex_adjust_pi(struct task_struct *task)
  *                       or TASK_UNINTERRUPTIBLE)
  * @timeout:             the pre-initialized and started timer, or NULL for none
  * @waiter:              the pre-initialized rt_mutex_waiter
- * @detect_deadlock:     passed to task_blocks_on_rt_mutex
  *
  * lock->wait_lock must be held by the caller.
  */
 static int __sched
 __rt_mutex_slowlock(struct rt_mutex *lock, int state,
                     struct hrtimer_sleeper *timeout,
-                    struct rt_mutex_waiter *waiter,
-                    int detect_deadlock)
+                    struct rt_mutex_waiter *waiter)
 {
         int ret = 0;
 
         for (;;) {
                 /* Try to acquire the lock: */
-                if (try_to_take_rt_mutex(lock))
+                if (try_to_take_rt_mutex(lock, current, waiter))
                         break;
 
                 /*
@@ -645,39 +599,11 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state,
                                 break;
                 }
 
-                /*
-                 * waiter->task is NULL the first time we come here and
-                 * when we have been woken up by the previous owner
-                 * but the lock got stolen by a higher prio task.
-                 */
-                if (!waiter->task) {
-                        ret = task_blocks_on_rt_mutex(lock, waiter, current,
-                                                      detect_deadlock);
-                        /*
-                         * If we got woken up by the owner then start loop
-                         * all over without going into schedule to try
-                         * to get the lock now:
-                         */
-                        if (unlikely(!waiter->task)) {
-                                /*
-                                 * Reset the return value. We might
-                                 * have returned with -EDEADLK and the
-                                 * owner released the lock while we
-                                 * were walking the pi chain.
-                                 */
-                                ret = 0;
-                                continue;
-                        }
-                        if (unlikely(ret))
-                                break;
-                }
-
                 raw_spin_unlock(&lock->wait_lock);
 
                 debug_rt_mutex_print_deadlock(waiter);
 
-                if (waiter->task)
-                        schedule_rt_mutex(lock);
+                schedule_rt_mutex(lock);
 
                 raw_spin_lock(&lock->wait_lock);
                 set_current_state(state);
@@ -698,12 +624,11 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
         int ret = 0;
 
         debug_rt_mutex_init_waiter(&waiter);
-        waiter.task = NULL;
 
         raw_spin_lock(&lock->wait_lock);
 
         /* Try to acquire the lock again: */
-        if (try_to_take_rt_mutex(lock)) {
+        if (try_to_take_rt_mutex(lock, current, NULL)) {
                 raw_spin_unlock(&lock->wait_lock);
                 return 0;
         }
@@ -717,12 +642,14 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
                         timeout->task = NULL;
         }
 
-        ret = __rt_mutex_slowlock(lock, state, timeout, &waiter,
-                                  detect_deadlock);
+        ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
+
+        if (likely(!ret))
+                ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
 
         set_current_state(TASK_RUNNING);
 
-        if (unlikely(waiter.task))
+        if (unlikely(ret))
                 remove_waiter(lock, &waiter);
 
         /*
@@ -737,14 +664,6 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
         if (unlikely(timeout))
                 hrtimer_cancel(&timeout->timer);
 
-        /*
-         * Readjust priority, when we did not get the lock. We might
-         * have been the pending owner and boosted. Since we did not
-         * take the lock, the PI boost has to go.
-         */
-        if (unlikely(ret))
-                rt_mutex_adjust_prio(current);
-
         debug_rt_mutex_free_waiter(&waiter);
 
         return ret;
@@ -762,7 +681,7 @@ rt_mutex_slowtrylock(struct rt_mutex *lock)
 
         if (likely(rt_mutex_owner(lock) != current)) {
 
-                ret = try_to_take_rt_mutex(lock);
+                ret = try_to_take_rt_mutex(lock, current, NULL);
                 /*
                  * try_to_take_rt_mutex() sets the lock waiters
                  * bit unconditionally. Clean this up.
@@ -992,7 +911,7 @@ void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
 {
         __rt_mutex_init(lock, NULL);
         debug_rt_mutex_proxy_lock(lock, proxy_owner);
-        rt_mutex_set_owner(lock, proxy_owner, 0);
+        rt_mutex_set_owner(lock, proxy_owner);
         rt_mutex_deadlock_account_lock(lock, proxy_owner);
 }
 
@@ -1008,7 +927,7 @@ void rt_mutex_proxy_unlock(struct rt_mutex *lock,
                            struct task_struct *proxy_owner)
 {
         debug_rt_mutex_proxy_unlock(lock);
-        rt_mutex_set_owner(lock, NULL, 0);
+        rt_mutex_set_owner(lock, NULL);
         rt_mutex_deadlock_account_unlock(proxy_owner);
 }
 
@@ -1034,20 +953,14 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
 
         raw_spin_lock(&lock->wait_lock);
 
-        mark_rt_mutex_waiters(lock);
-
-        if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
-                /* We got the lock for task. */
-                debug_rt_mutex_lock(lock);
-                rt_mutex_set_owner(lock, task, 0);
+        if (try_to_take_rt_mutex(lock, task, NULL)) {
                 raw_spin_unlock(&lock->wait_lock);
-                rt_mutex_deadlock_account_lock(lock, task);
                 return 1;
         }
 
         ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
 
-        if (ret && !waiter->task) {
+        if (ret && !rt_mutex_owner(lock)) {
                 /*
                  * Reset the return value. We might have
                  * returned with -EDEADLK and the owner
@@ -1056,6 +969,10 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
                  */
                 ret = 0;
         }
+
+        if (unlikely(ret))
+                remove_waiter(lock, waiter);
+
         raw_spin_unlock(&lock->wait_lock);
 
         debug_rt_mutex_print_deadlock(waiter);
@@ -1110,12 +1027,11 @@ int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
 
         set_current_state(TASK_INTERRUPTIBLE);
 
-        ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter,
-                                  detect_deadlock);
+        ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
 
         set_current_state(TASK_RUNNING);
 
-        if (unlikely(waiter->task))
+        if (unlikely(ret))
                 remove_waiter(lock, waiter);
 
         /*
@@ -1126,13 +1042,5 @@ int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
 
         raw_spin_unlock(&lock->wait_lock);
 
-        /*
-         * Readjust priority, when we did not get the lock. We might have been
-         * the pending owner and boosted. Since we did not take the lock, the
-         * PI boost has to go.
-         */
-        if (unlikely(ret))
-                rt_mutex_adjust_prio(current);
-
         return ret;
 }