Index: Lib/threading.py
===================================================================
--- Lib/threading.py	(revision 51000)
+++ Lib/threading.py	(working copy)
@@ -537,6 +537,16 @@
         _active_limbo_lock.acquire()
         try:
             try:
+                # We need to turn off any tracing/profiling functions for
+                # this thread, now. If we don't then when we delete
+                # _active[_get_ident()], if either of the functions call
+                # currentThread(), a _DummyThread object will be created,
+                # which will try to acquire _active_limbo_lock which we're
+                # currently holding. 
+                if _trace_hook:
+                    _sys.settrace(None)
+                if _profile_hook:
+                    _sys.setprofile(None)
                 del _active[_get_ident()]
             except KeyError:
                 if 'dummy_threading' not in _sys.modules:
Index: Lib/test/test_threading.py
===================================================================
--- Lib/test/test_threading.py	(revision 51000)
+++ Lib/test/test_threading.py	(working copy)
@@ -121,6 +121,28 @@
                                 threading._DummyThread))
         del threading._active[tid]
 
+    def test_trace_and_profile_func(self):
+        # Make sure that a thread can successfully delete itself from
+        # the _active dictionary even if tracing/profiling functions are
+        # being used.
+        def trace(frame, event, arg):
+            id = threading.currentThread().getName()
+            return trace
+
+        def target():
+            for i in range(100):
+                pass
+
+        threading.settrace(trace)
+        t1 = threading.Thread(target=target)
+        t1.start()
+        t1.join()
+
+        threading.setprofile(trace)
+        t2 = threading.Thread(target=target)
+        t2.start()
+        t2.join()
+
 def test_main():
     test.test_support.run_unittest(ThreadTests)