[Bug #19114] Fix for multiple calls of TracePoint#enable

test/ruby/test_settracefunc.rb

@@ -2459,6 +2459,18 @@ CODE
     assert_equal [:tp1, 1, 2, :tp2, 3], events
   end
 
+  def test_multiple_enable
+    ary = []
+    trace = TracePoint.new(:call) do |tp|
+      ary << tp.method_id
+    end
+    trace.enable
+    trace.enable
+    foo
+    trace.disable
+    assert_equal(1, ary.count(:foo), '[Bug #19114]')
+  end
+
   def test_multiple_tracepoints_same_bmethod
     events = []
     tp1 = TracePoint.new(:return) do |tp|

vm_trace.c

@@ -1197,6 +1197,10 @@ rb_tracepoint_enable(VALUE tpval)
         rb_raise(rb_eArgError, "can't nest-enable a targeting TracePoint");
     }
 
+    if (tp->tracing) {
+        return Qundef;
+    }
+
     if (tp->target_th) {
         rb_thread_add_event_hook2(tp->target_th->self, (rb_event_hook_func_t)tp_call_trace, tp->events, tpval,
                                   RUBY_EVENT_HOOK_FLAG_SAFE | RUBY_EVENT_HOOK_FLAG_RAW_ARG);