Upgrade to 4.4.50-rt62

[kvmfornfv.git] / kernel / kernel / locking / rtmutex.c

diff --git a/kernel/kernel/locking/rtmutex.c b/kernel/kernel/locking/rtmutex.c
index 30777e8..86a78c0 100644 (file)
--- a/kernel/kernel/locking/rtmutex.c
+++ b/kernel/kernel/locking/rtmutex.c
@@ -71,8 +71,72 @@ static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
 
 static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
 {
-       if (!rt_mutex_has_waiters(lock))
-               clear_rt_mutex_waiters(lock);
+       unsigned long owner, *p = (unsigned long *) &lock->owner;
+
+       if (rt_mutex_has_waiters(lock))
+               return;
+
+       /*
+        * The rbtree has no waiters enqueued, now make sure that the
+        * lock->owner still has the waiters bit set, otherwise the
+        * following can happen:
+        *
+        * CPU 0        CPU 1           CPU2
+        * l->owner=T1
+        *              rt_mutex_lock(l)
+        *              lock(l->lock)
+        *              l->owner = T1 | HAS_WAITERS;
+        *              enqueue(T2)
+        *              boost()
+        *                unlock(l->lock)
+        *              block()
+        *
+        *                              rt_mutex_lock(l)
+        *                              lock(l->lock)
+        *                              l->owner = T1 | HAS_WAITERS;
+        *                              enqueue(T3)
+        *                              boost()
+        *                                unlock(l->lock)
+        *                              block()
+        *              signal(->T2)    signal(->T3)
+        *              lock(l->lock)
+        *              dequeue(T2)
+        *              deboost()
+        *                unlock(l->lock)
+        *                              lock(l->lock)
+        *                              dequeue(T3)
+        *                               ==> wait list is empty
+        *                              deboost()
+        *                               unlock(l->lock)
+        *              lock(l->lock)
+        *              fixup_rt_mutex_waiters()
+        *                if (wait_list_empty(l) {
+        *                  l->owner = owner
+        *                  owner = l->owner & ~HAS_WAITERS;
+        *                    ==> l->owner = T1
+        *                }
+        *                              lock(l->lock)
+        * rt_mutex_unlock(l)           fixup_rt_mutex_waiters()
+        *                                if (wait_list_empty(l) {
+        *                                  owner = l->owner & ~HAS_WAITERS;
+        * cmpxchg(l->owner, T1, NULL)
+        *  ===> Success (l->owner = NULL)
+        *
+        *                                  l->owner = owner
+        *                                    ==> l->owner = T1
+        *                                }
+        *
+        * With the check for the waiter bit in place T3 on CPU2 will not
+        * overwrite. All tasks fiddling with the waiters bit are
+        * serialized by l->lock, so nothing else can modify the waiters
+        * bit. If the bit is set then nothing can change l->owner either
+        * so the simple RMW is safe. The cmpxchg() will simply fail if it
+        * happens in the middle of the RMW because the waiters bit is
+        * still set.
+        */
+       owner = READ_ONCE(*p);
+       if (owner & RT_MUTEX_HAS_WAITERS)
+               WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
 }
 
 static int rt_mutex_real_waiter(struct rt_mutex_waiter *waiter)
@@ -939,13 +1003,14 @@ static inline void rt_spin_lock_fastlock(struct rt_mutex *lock,
                slowfn(lock, do_mig_dis);
 }
 
-static inline void rt_spin_lock_fastunlock(struct rt_mutex *lock,
-                                          void  (*slowfn)(struct rt_mutex *lock))
+static inline int rt_spin_lock_fastunlock(struct rt_mutex *lock,
+                                          int  (*slowfn)(struct rt_mutex *lock))
 {
-       if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
+       if (likely(rt_mutex_cmpxchg_release(lock, current, NULL))) {
                rt_mutex_deadlock_account_unlock(current);
-       else
-               slowfn(lock);
+               return 0;
+       }
+       return slowfn(lock);
 }
 #ifdef CONFIG_SMP
 /*
@@ -1086,7 +1151,7 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
 /*
  * Slow path to release a rt_mutex spin_lock style
  */
-static void  noinline __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
+static int noinline __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
 {
        unsigned long flags;
        WAKE_Q(wake_q);
@@ -1101,7 +1166,7 @@ static void  noinline __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
        if (!rt_mutex_has_waiters(lock)) {
                lock->owner = NULL;
                raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
-               return;
+               return 0;
        }
 
        mark_wakeup_next_waiter(&wake_q, &wake_sleeper_q, lock);
@@ -1112,6 +1177,33 @@ static void  noinline __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
 
        /* Undo pi boosting.when necessary */
        rt_mutex_adjust_prio(current);
+       return 0;
+}
+
+static int noinline __sched rt_spin_lock_slowunlock_no_deboost(struct rt_mutex *lock)
+{
+       unsigned long flags;
+       WAKE_Q(wake_q);
+       WAKE_Q(wake_sleeper_q);
+
+       raw_spin_lock_irqsave(&lock->wait_lock, flags);
+
+       debug_rt_mutex_unlock(lock);
+
+       rt_mutex_deadlock_account_unlock(current);
+
+       if (!rt_mutex_has_waiters(lock)) {
+               lock->owner = NULL;
+               raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+               return 0;
+       }
+
+       mark_wakeup_next_waiter(&wake_q, &wake_sleeper_q, lock);
+
+       raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+       wake_up_q(&wake_q);
+       wake_up_q_sleeper(&wake_sleeper_q);
+       return 1;
 }
 
 void __lockfunc rt_spin_lock__no_mg(spinlock_t *lock)
@@ -1166,6 +1258,17 @@ void __lockfunc rt_spin_unlock(spinlock_t *lock)
 }
 EXPORT_SYMBOL(rt_spin_unlock);
 
+int __lockfunc rt_spin_unlock_no_deboost(spinlock_t *lock)
+{
+       int ret;
+
+       /* NOTE: we always pass in '1' for nested, for simplicity */
+       spin_release(&lock->dep_map, 1, _RET_IP_);
+       ret = rt_spin_lock_fastunlock(&lock->lock, rt_spin_lock_slowunlock_no_deboost);
+       migrate_enable();
+       return ret;
+}
+
 void __lockfunc __rt_spin_unlock(struct rt_mutex *lock)
 {
        rt_spin_lock_fastunlock(lock, rt_spin_lock_slowunlock);