fix a bug of inplace

python/paddle/v2/fluid/backward.py

@@ -99,6 +99,9 @@ def _append_backward_ops_(target,
                     attrs={}), idx))
                 var_inputs[var_name] = [var_name]
         for var_name in op_desc.output_arg_names():
+            if var_name in op_desc.input_arg_names():
+                # in place operator
+                continue
             if var_name == core.empty_var_name() or len(var_inputs[
                     var_name]) == 0:
                 # it's the first time we get the variable
@@ -221,6 +224,9 @@ def append_backward(loss, parameter_list=None, no_grad_set=None):
                 if var.stop_gradient:
                     block_no_grad_set.add(_append_grad_suffix_(var.name))
             no_grad_set[block.idx] = block_no_grad_set
+    else:
+        # FIX ME
+        no_grad_set = {0: no_grad_set}
 
     grad_info_map = dict()
     root_block = program.block(0)