9959 pthread_mutex_init should initialize mutex appropriately for robust mutex_init

*** 224,233 ****
--- 224,250 ----
          } else {
                  type = PTHREAD_PROCESS_PRIVATE | PTHREAD_MUTEX_DEFAULT |
                      PTHREAD_PRIO_NONE | PTHREAD_MUTEX_STALLED;
          }
  
+         /*
+          * POSIX mutexes (this interface) make no guarantee about the state of
+          * the mutex before pthread_mutex_init(3C) is called.  Sun mutexes, upon
+          * which these are built and which mutex_init(3C) below represents
+          * require that a robust mutex be initialized to all 0s _prior_ to
+          * mutex_init() being called, and that mutex_init() of an initialized
+          * mutex return EBUSY.
+          *
+          * We respect both these behaviors by zeroing the mutex here in the
+          * POSIX implementation if and only if the mutex magic is incorrect,
+          * and the mutex is robust.
+          */
+         if (((type & PTHREAD_MUTEX_ROBUST) != 0) &&
+             (((mutex_t *)mutex)->mutex_magic != MUTEX_MAGIC)) {
+                 (void) memset(mutex, 0, sizeof (*mutex));
+         }
+ 
          return (mutex_init((mutex_t *)mutex, type, &prioceiling));
  }
  
  /*
   * pthread_mutex_setprioceiling: sets the prioceiling.