Update some comments

sched/pthread/pthread_mutexlock.c

@@ -136,8 +136,13 @@ int pthread_mutex_lock(FAR pthread_mutex_t *mutex)
           else
 #endif
             {
-              /* No, then we would deadlock... return an error (default behavior
-               * is like PTHREAD_MUTEX_ERRORCHECK)
+              /* No, then we would deadlock... return an error (default
+               * behavior is like PTHREAD_MUTEX_ERRORCHECK)
+               *
+               * NOTE:  This is non-compliant behavior for the case of a
+               * NORMAL mutex.  In that case, it the deadlock condition should
+               * not be detected and the thread should be permitted to
+               * deadlock.
                */
 
               serr("ERROR: Returning EDEADLK\n");
@@ -169,4 +174,3 @@ int pthread_mutex_lock(FAR pthread_mutex_t *mutex)
   sinfo("Returning %d\n", ret);
   return ret;
 }
-

sched/pthread/pthread_mutexunlock.c

@@ -100,13 +100,22 @@ int pthread_mutex_unlock(FAR pthread_mutex_t *mutex)
 
       if (mutex->pid != (int)getpid())
         {
-          /* No... return an error (default behavior is like PTHREAD_MUTEX_ERRORCHECK) */
+          /* No... return an EPERM error.
+           *
+           * Per POSIX:  "EPERM should be returned if the mutex type is
+           * PTHREAD_MUTEX_ERRORCHECK or PTHREAD_MUTEX_RECURSIVE, or the
+           * mutex is a robust mutex, and the current thread does not own
+           * the mutex."
+           *
+           * For the case of the non-robust PTHREAD_MUTEX_NORMAL mutex,
+           * the behavior is undefined.  Here we treat that type as though
+           * it were PTHREAD_MUTEX_ERRORCHECK type and just return an error.
+           */
 
           serr("ERROR: Holder=%d returning EPERM\n", mutex->pid);
           ret = EPERM;
         }
 
-
       /* Yes, the caller owns the semaphore.. Is this a recursive mutex? */
 
 #ifdef CONFIG_MUTEX_TYPES
@@ -116,6 +125,7 @@ int pthread_mutex_unlock(FAR pthread_mutex_t *mutex)
            * the mutex lock, just decrement the count of locks held, and return
            * success.
            */
+
           mutex->nlocks--;
         }
 #endif
@@ -134,6 +144,7 @@ int pthread_mutex_unlock(FAR pthread_mutex_t *mutex)
 #endif
           ret = pthread_givesemaphore((FAR sem_t *)&mutex->sem);
         }
+
       sched_unlock();
     }