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aaa_diameter_swx: Avoid answering RTR with Success if already deregistering

When receiving an SWx RTR on our osmo-epdg (epdg+AAA), we initiate the
deregistration against peer nodes on other interfaces and answer with SWx RTA.

If a subsequent RTR for the subscriber arrives on the interface while
the deregistration is in progress, we'd answer with RTA Result-Code 2001
SUCCESS. Let's instead answer already as if we didn't know about the
subscriber, since it will end up being freed in a short span of time and
nothing can be done about it.

Related: OS#6796
Change-Id: I0ed13e9503ec380ce4331c662ca3eb966ccbda92
---
M src/aaa_diameter_swx_cb.erl
M src/aaa_ue_fsm.erl
2 files changed, 21 insertions(+), 9 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/erlang/osmo-epdg refs/changes/03/41303/1

diff --git a/src/aaa_diameter_swx_cb.erl b/src/aaa_diameter_swx_cb.erl
index 3ae11f0..f8ebd08 100644
--- a/src/aaa_diameter_swx_cb.erl
+++ b/src/aaa_diameter_swx_cb.erl
@@ -149,14 +149,26 @@
             case DeregReason of
                 #'Deregistration-Reason'{'Reason-Code' = ?'REASON-CODE_PERMANENT_TERMINATION'} ->
                     case aaa_ue_fsm:ev_rx_swx_rtr(Pid) of
-                        {error, _} -> aaa_ue_fsm:stop(Pid);
-                        _ -> ok
+                        {error, dereg_in_progress} ->
+                            Res = [],
+                            %% TS 29.229 6.2.2.1 DIAMETER_ERROR_USER_UNKNOWN
+                            ERes = #'Experimental-Result'{'Vendor-Id' = ?VENDOR_ID_3GPP,
+                                                        'Experimental-Result-Code' = 5001};
+                        {error, _} ->
+                            aaa_ue_fsm:stop(Pid), % unknown error, make sure we tear down.
+                            Res = [],
+                            %% TS 29.229 6.2.2.1 DIAMETER_ERROR_USER_UNKNOWN
+                            ERes = #'Experimental-Result'{'Vendor-Id' = ?VENDOR_ID_3GPP,
+                                                        'Experimental-Result-Code' = 5001};
+                        _ ->
+                            Res = 2001, %% Success
+                            ERes = []
                     end;
                 _ ->
-                    aaa_ue_fsm:stop(Pid)
-            end,
-            Res = 2001, %% Success
-            ERes = [];
+                    aaa_ue_fsm:stop(Pid),
+                    Res = 2001, %% Success
+                    ERes = []
+            end;
         undefined ->
             Res = [],
             %% TS 29.229 6.2.2.1 DIAMETER_ERROR_USER_UNKNOWN
diff --git a/src/aaa_ue_fsm.erl b/src/aaa_ue_fsm.erl
index fa1c807..91830d9 100644
--- a/src/aaa_ue_fsm.erl
+++ b/src/aaa_ue_fsm.erl
@@ -451,7 +451,7 @@
 state_authenticated_wait_swx_saa({call, From}, rx_swx_rtr, Data) ->
     lager:info("ue_fsm state_authenticated_wait_swx_saa event=rx_swx_rtr ~p~n", [Data]),
     %% We are already tearing down in an ordered manner, accept and do nothing.
-    {keep_state, Data, [{reply,From,ok}]};
+    {keep_state, Data, [{reply,From,{error,dereg_in_progress}}]}.
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% state_dereg_net_initiated_wait_s6b_asa:
@@ -469,7 +469,7 @@
 state_dereg_net_initiated_wait_s6b_asa({call, From}, rx_swx_rtr, Data) ->
     lager:info("ue_fsm state_dereg_net_initiated_wait_s6b_asa event=rx_swx_rtr ~p~n", [Data]),
     %% We are already tearing down in an ordered manner, accept and do nothing.
-    {keep_state, Data, [{reply,From,ok}]};
+    {keep_state, Data, [{reply,From,{error,dereg_in_progress}}]};
 
 state_dereg_net_initiated_wait_s6b_asa({call, From}, Ev, Data) ->
         lager:notice("ue_fsm state_dereg_net_initiated_wait_s6b_asa: Unexpected call event ~p, ~p~n", [Ev, Data]),
@@ -494,7 +494,7 @@
 state_dereg_net_initiated_wait_swm_asa({call, From}, rx_swx_rtr, Data) ->
     lager:info("ue_fsm state_dereg_net_initiated_wait_swm_asa event=rx_swx_rtr ~p~n", [Data]),
     %% We are already tearing down in an ordered manner, accept and do nothing.
-    {keep_state, Data, [{reply,From,ok}]};
+    {keep_state, Data, [{reply,From,{error,dereg_in_progress}}]};
 
 state_dereg_net_initiated_wait_swm_asa({call, From}, Ev, Data) ->
         lager:notice("ue_fsm state_dereg_net_initiated_wait_swm_asa: Unexpected call event ~p, ~p~n", [Ev, Data]),

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