--- xnu/xnu-201.42.3/iokit/Kernel/IOLocks.cpp
+++ xnu/xnu-201.5/iokit/Kernel/IOLocks.cpp
@@ -156,13 +156,13 @@
     
     res = thread_block(0);
 
-    // Must re-establish the recursive lock no matter why we woke up
-    // otherwise we would potentially leave the return path corrupted.
-    mutex_lock(lock->mutex);
-    assert(lock->thread == 0);
-    assert(lock->count == 0);
-    lock->thread = IOThreadSelf();
-    lock->count = count;
+    if (THREAD_AWAKENED == res) {
+        mutex_lock(lock->mutex);
+        assert(lock->thread == 0);
+        assert(lock->count == 0);
+        lock->thread = IOThreadSelf();
+        lock->count = count;
+    }
 
     return res;
 }