Reset cluster_change_permitted when becoming leader

As if there had been a leader change before this could reset to true
even before the leader has fully applied it's noop command for the new
term. This could result in occasional stale consistent read results.

src/ra_server.erl

@@ -1483,7 +1483,8 @@ machine_query(QueryFun, #{cfg := #cfg{effective_machine_module = MacMod},
 
 become(leader, #{cluster := Cluster, log := Log0} = State) ->
     Log = ra_log:release_resources(maps:size(Cluster) + 2, random, Log0),
-    State#{log => Log};
+    State#{log => Log,
+           cluster_change_permitted => false};
 become(follower, #{log := Log0} = State) ->
     %% followers should only ever need a single segment open at any one
     %% time

test/ra_SUITE.erl

@@ -45,6 +45,7 @@ all_tests() ->
      local_query_stale,
      members,
      consistent_query,
+     consistent_query_after_restart,
      consistent_query_minority,
      consistent_query_leader_change,
      consistent_query_stale,
@@ -544,6 +545,27 @@ consistent_query(Config) ->
     {ok, 14, Leader} = ra:consistent_query(A, fun(S) -> S end),
     terminate_cluster(Cluster).
 
+new_value(A, _) ->
+    A.
+
+consistent_query_after_restart(Config) ->
+    DataDir = filename:join([?config(priv_dir, Config), "data"]),
+    [A, B]  = Cluster = start_local_cluster(2, ?config(test_name, Config),
+                                            {simple, fun ?MODULE:new_value/2, 0}),
+    %% this test occasionally reproduces a stale read bug after a restart
+    %% NB: occasionally....
+    [begin
+         {ok, _, _} = ra:process_command(A, N, ?PROCESS_COMMAND_TIMEOUT),
+         application:stop(ra),
+         restart_ra(DataDir),
+         ok = ra:restart_server(A),
+         ok = ra:restart_server(B),
+         ?assertMatch({ok, N, _}, ra:consistent_query(A, fun(S) -> S end))
+     end || N <- lists:seq(1, 30)],
+
+    terminate_cluster(Cluster),
+    ok.
+
 consistent_query_minority(Config) ->
     [A, _, _]  = Cluster = start_local_cluster(3, ?config(test_name, Config),
                                                add_machine()),

test/ra_log_segment_writer_SUITE.erl

@@ -5,6 +5,7 @@
 %% Copyright (c) 2017-2022 VMware, Inc. or its affiliates.  All rights reserved.
 %%
 -module(ra_log_segment_writer_SUITE).
+-compile(nowarn_export_all).
 -compile(export_all).
 
 -include_lib("common_test/include/ct.hrl").