@@ -349,12 +349,14 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
 
 /*
  * Return the folowing three values depending on the lock owner state.
+ *   2	when owner is currently NULL
  *   1	when owner changes and no reader is detected yet.
  *   0	when owner changes and the new owner may be a reader.
  *  -1	when optimistic spinning has to stop because either the owner stops
  *	running, is unknown, or its timeslice has been used up.
  */
 enum owner_state {
+	OWNER_NULL = 2,
 	OWNER_SPINNABLE = 1,
 	OWNER_READER = 0,
 	OWNER_NONSPINNABLE = -1,

@@ -405,7 +407,8 @@ static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem)
 	owner = rwsem_get_owner(sem);
 	if (!is_rwsem_owner_spinnable(owner))
 		return OWNER_NONSPINNABLE;
-	return is_rwsem_owner_reader(owner) ? OWNER_READER : OWNER_SPINNABLE;
+	return !owner ? OWNER_NULL :
+	       is_rwsem_owner_reader(owner) ? OWNER_READER : OWNER_SPINNABLE;
 }
 
 static bool rwsem_optimistic_spin(struct rw_semaphore *sem, const long wlock)

@@ -442,12 +445,13 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem, const long wlock)
 			break;
 
 		/*
-		 * When there's no owner, we might have preempted between the
-		 * owner acquiring the lock and setting the owner field. If
-		 * we're an RT task that will live-lock because we won't let
-		 * the owner complete.
+		 * An RT task cannot do optimistic spinning if it cannot
+		 * be sure the lock holder is running. When there's no owner
+		 * or is reader-owned, an RT task has to stop spinning or
+		 * live-lock may happen if the current task and the lock
+		 * holder happen to run in the same CPU.
 		 */
-		if (!rwsem_get_owner(sem) &&
+		if ((owner_state != OWNER_SPINNABLE) &&
 		   (need_resched() || rt_task(current)))
 			break;