fix(exclusive): allow the same client to resubscribe to an existing exclusive topic

apps/emqx/src/emqx_exclusive_subscription.erl

@@ -117,6 +117,13 @@ try_subscribe(ClientId, Topic) ->
                 write
             ),
             allow;
+        [#exclusive_subscription{clientid = ClientId, topic = Topic}] ->
+            %% Fixed the issue-13476
+            %% In this feature, the user must manually call `unsubscribe` to release the lock,
+            %% but sometimes the node may go down for some reason,
+            %% then the client will reconnect to this node and resubscribe.
+            %% We need to allow resubscription, otherwise the lock will never be released.
+            allow;
         [_] ->
             deny
     end.

apps/emqx/test/emqx_exclusive_sub_SUITE.erl

@@ -56,6 +56,8 @@ t_exclusive_sub(_) ->
     {ok, _} = emqtt:connect(C1),
     ?CHECK_SUB(C1, 0),
 
+    ?CHECK_SUB(C1, 0),
+
     {ok, C2} = emqtt:start_link([
         {clientid, <<"client2">>},
         {clean_start, false},