From 6073d37a5a0691704d0fa1a5ff9289ba9e35c8ed Mon Sep 17 00:00:00 2001
From: Siri Hansen <siri@erlang.org>
Date: Fri, 14 Sep 2018 14:12:13 +0200
Subject: [logger] Read config before terminating handler process

When a handler process is terminated due to overload, it reads its
configuration from the configuration database, so it can be restarted
with the same configuration after a small delay. This was earlier done
in a different process, which was spawned off from the terminate
function. This caused a race condition, where in some cases, the
configuration was already removed before it could be read.

The reason for spawning off a process, is to avoid a deadlock due to
the call to logger:remove_handler/1.

This commit moves the call to logger:get_handler_config/1 back to the
handler process - to ensure that the data is still there, but keeps
the call to logger:remove_handler/1 in the spawned off process - to
avoid deadlock.
---
 lib/kernel/src/logger_disk_log_h.erl | 3 ++-
 lib/kernel/src/logger_h_common.erl   | 3 ++-
 lib/kernel/src/logger_std_h.erl      | 3 ++-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/kernel/src/logger_disk_log_h.erl b/lib/kernel/src/logger_disk_log_h.erl
index 26375373aa..a8f141f135 100644
--- a/lib/kernel/src/logger_disk_log_h.erl
+++ b/lib/kernel/src/logger_disk_log_h.erl
@@ -426,8 +426,9 @@ terminate(Reason, State = #{id := Name}) ->
     _ = logger_h_common:cancel_timer(maps:get(rep_sync_tref, State,
                                               undefined)),
     _ = close_disk_log(Name, normal),
+    ok = logger_h_common:stop_or_restart(Name, Reason, State),
     unregister(?name_to_reg_name(?MODULE, Name)),
-    logger_h_common:stop_or_restart(Name, Reason, State).
+    ok.
 
 code_change(_OldVsn, State, _Extra) ->
     {ok, State}.
diff --git a/lib/kernel/src/logger_h_common.erl b/lib/kernel/src/logger_h_common.erl
index 2818a460f1..38ac7d8ffc 100644
--- a/lib/kernel/src/logger_h_common.erl
+++ b/lib/kernel/src/logger_h_common.erl
@@ -294,6 +294,7 @@ stop_or_restart(Name, {shutdown,Reason={overloaded,_Name,_QLen,_Mem}},
     %% and set a restart timer. A separate process must perform this
     %% in order to avoid deadlock.
     HandlerPid = self(),
+    ConfigResult = logger:get_handler_config(Name),
     RemoveAndRestart =
         fun() ->
                 MRef = erlang:monitor(process, HandlerPid),
@@ -304,7 +305,7 @@ stop_or_restart(Name, {shutdown,Reason={overloaded,_Name,_QLen,_Mem}},
                         error_notify(Reason),
                         exit(HandlerPid, kill)
                 end,
-                case logger:get_handler_config(Name) of
+                case ConfigResult of
                     {ok,#{module:=HMod}=HConfig} when is_integer(RestartAfter) ->
                         _ = logger:remove_handler(Name),
                         _ = timer:apply_after(RestartAfter, logger, add_handler,
diff --git a/lib/kernel/src/logger_std_h.erl b/lib/kernel/src/logger_std_h.erl
index 5dc4bc91ad..66fa6b6ab6 100644
--- a/lib/kernel/src/logger_std_h.erl
+++ b/lib/kernel/src/logger_std_h.erl
@@ -415,8 +415,9 @@ terminate(Reason, State = #{id:=Name, file_ctrl_pid:=FWPid,
         false ->
             ok
     end,
+    ok = logger_h_common:stop_or_restart(Name, Reason, State),
     unregister(?name_to_reg_name(?MODULE, Name)),
-    logger_h_common:stop_or_restart(Name, Reason, State).
+    ok.
                                                   
 code_change(_OldVsn, State, _Extra) ->
     {ok, State}.
-- 
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