Fix missing monitor in diameter_reg

Commit fae8ca0c inadvertently removed the monitor at add/1 and
add_new/1. As a result, process death did not remove associations,
causing table diameter_reg to leak entries and stop/start of a service
to fail.

Add a testcase to detect the problem, which existing testcases miss.

2 files changed, 15 insertions, 2 deletions

diff --git a/lib/diameter/src/base/diameter_reg.erl b/lib/diameter/src/base/diameter_reg.erl
index bd5db54a5c..e0c41a2834 100644
--- a/lib/diameter/src/base/diameter_reg.erl
+++ b/lib/diameter/src/base/diameter_reg.erl
@@ -238,7 +238,11 @@ handle_call({add, Uniq, Key}, {Pid, _}, S) ->
     Rec = {Key, Pid},
     NS = flush(Uniq, Rec, S),  %% before insert
     {Res, New} = insert(Uniq, Rec),
-    {reply, Res, notify(add, New andalso Rec, NS)};
+    {reply, Res, notify(add, New andalso Rec, if New ->
+                                                      add_monitor(Pid, NS);
+                                                 true ->
+                                                      NS
+                                              end)};
 
 handle_call({remove, Key}, {Pid, _}, S) ->
     Rec = {Key, Pid},
diff --git a/lib/diameter/test/diameter_reg_SUITE.erl b/lib/diameter/test/diameter_reg_SUITE.erl
index e2a1ca00c3..cd9242faa8 100644
--- a/lib/diameter/test/diameter_reg_SUITE.erl
+++ b/lib/diameter/test/diameter_reg_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2016. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2017. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -34,6 +34,7 @@
 -export([add/1,
          add_new/1,
          remove/1,
+         down/1,
          terms/1,
          pids/1]).
 
@@ -56,6 +57,7 @@ tc() ->
     [add,
      add_new,
      remove,
+     down,
      terms,
      pids].
 
@@ -88,6 +90,13 @@ remove(_) ->
     [{Ref, Pid}] = ?reg:match(Ref),
     Pid = self().
 
+down(_) ->
+    Ref = make_ref(),
+    {_, MRef} = spawn_monitor(fun() -> ?reg:add_new(Ref), timer:sleep(1000) end),
+    receive {'DOWN', MRef, process, _, _} -> ok end,
+    timer:sleep(1000),
+    [] = ?reg:match(Ref).
+
 terms(_) ->
     Ref = make_ref(),
     true = ?reg:add_new(Ref),