--- xnu/xnu-201/iokit/Kernel/IOLocks.cpp
+++ xnu/xnu-517.7.21/iokit/Kernel/IOLocks.cpp
@@ -149,21 +149,16 @@
     assert(lock->thread == IOThreadSelf());
     assert(lock->count == 1 || interType == THREAD_UNINT);
     
-    assert_wait((event_t) event, (int) interType);
     lock->count = 0;
     lock->thread = 0;
-    mutex_unlock(lock->mutex);
-    
-    res = thread_block(0);
-
-    if (THREAD_AWAKENED == res) {
-        mutex_lock(lock->mutex);
-        assert(lock->thread == 0);
-        assert(lock->count == 0);
-        lock->thread = IOThreadSelf();
-        lock->count = count;
-    }
-
+    res = thread_sleep_mutex((event_t) event, lock->mutex, (int) interType);
+
+    // Must re-establish the recursive lock no matter why we woke up
+    // otherwise we would potentially leave the return path corrupted.
+    assert(lock->thread == 0);
+    assert(lock->count == 0);
+    lock->thread = IOThreadSelf();
+    lock->count = count;
     return res;
 }