From d89925ce7b7222dd2f871054a6a254aad3e62ac7 Mon Sep 17 00:00:00 2001
From: Thales Macedo Garitezi <thalesmg@gmail.com>
Date: Tue, 22 Feb 2022 16:31:35 -0300
Subject: [PATCH 1/3] fix(sys_mon): guard before calling `erlang:port_info`

Sometimes, the `emqx_sys_mon:procinfo/1` might be called with
something that is not a port, like `[]`.  Not sure on the conditions
for this to happen.

```
2022-02-18T20:05:02.671592+00:00 [error] Generic server emqx_sys_mon terminating. Reason: {badarg,[{erlang,port_info,[[]],[{error_info,#{module => erl_erts_errors}}]},{emqx_sys_mon,portinfo,1,[{file,"/emqx/apps/emqx/src/emqx_sys_mon.erl"},{line,205}]},{emqx_sys_mon,'-handle_info/2-fun-5-',2,[{file,"/emqx/apps/emqx/src/emqx_sys_mon.erl"},{line,150}]},{emqx_sys_mon,suppress,3,[{file,"/emqx/apps/emqx/src/emqx_sys_mon.erl"},{line,184}]},{gen_server,try_dispatch,4,[{file,"gen_server.erl"},{line,695}]},{gen_server,handle_msg,6,[{file,"gen_server.erl"},{line,771}]},{proc_lib,wake_up,3,[{file,"proc_lib.erl"},{line,236}]}]}. Last message: {monitor,<0.7796.0>,busy_dist_port,[]}. State: #{events => [{busy_dist_port,#Port<0.127>}],timer => #Ref<0.2758388682.1853620226.133920>}.
```
---
 apps/emqx/src/emqx_sys_mon.erl        | 7 ++++++-
 apps/emqx/test/emqx_sys_mon_SUITE.erl | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/apps/emqx/src/emqx_sys_mon.erl b/apps/emqx/src/emqx_sys_mon.erl
index 1f8f04d97..1df9ec604 100644
--- a/apps/emqx/src/emqx_sys_mon.erl
+++ b/apps/emqx/src/emqx_sys_mon.erl
@@ -202,7 +202,12 @@ get_proc_lib_initial_call(Pid) ->
     end.
 
 portinfo(Port) ->
-    [{port, Port} | erlang:port_info(Port)].
+    PortInfo =
+        case is_port(Port) andalso erlang:port_info(Port) of
+            L when is_list(L) -> L;
+            _ -> []
+        end,
+    [{port, Port} | PortInfo].
 
 safe_publish(Event, WarnMsg) ->
     Topic = emqx_topic:systop(lists:concat(['sysmon/', Event])),
diff --git a/apps/emqx/test/emqx_sys_mon_SUITE.erl b/apps/emqx/test/emqx_sys_mon_SUITE.erl
index 8e4bd65db..31acd885f 100644
--- a/apps/emqx/test/emqx_sys_mon_SUITE.erl
+++ b/apps/emqx/test/emqx_sys_mon_SUITE.erl
@@ -35,6 +35,11 @@
                     {self(), busy_port,
                      fmt("busy_port warning: suspid = ~p, port = ~p",
                          [self(), ?FAKE_PORT]), ?FAKE_PORT},
+                    %% for the case when the port is missing, for some
+                    %% reason.
+                    {self(), busy_port,
+                     fmt("busy_port warning: suspid = ~p, port = ~p",
+                         [self(), []]), []},
                     {self(), busy_dist_port,
                      fmt("busy_dist_port warning: suspid = ~p, port = ~p",
                          [self(), ?FAKE_PORT]), ?FAKE_PORT},

From 427866f8adb5376e0da31acd37f9e8e6fd947599 Mon Sep 17 00:00:00 2001
From: Thales Macedo Garitezi <thalesmg@gmail.com>
Date: Thu, 24 Feb 2022 15:13:18 -0300
Subject: [PATCH 2/3] test(sys_mon): add test for closed port

---
 apps/emqx/test/emqx_sys_mon_SUITE.erl | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/apps/emqx/test/emqx_sys_mon_SUITE.erl b/apps/emqx/test/emqx_sys_mon_SUITE.erl
index 31acd885f..c14074f0d 100644
--- a/apps/emqx/test/emqx_sys_mon_SUITE.erl
+++ b/apps/emqx/test/emqx_sys_mon_SUITE.erl
@@ -125,6 +125,16 @@ t_sys_mon(_Config) ->
               validate_sys_mon_info(PidOrPort, SysMonName, ValidateInfo, InfoOrPort)
       end, ?INPUTINFO).
 
+%% Existing port, but closed.
+t_sys_mon_dead_port(_Config) ->
+    process_flag(trap_exit, true),
+    Port = dead_port(),
+    {PidOrPort, SysMonName, ValidateInfo, InfoOrPort} =
+        {self(), busy_port,
+         fmt("busy_port warning: suspid = ~p, port = ~p",
+             [self(), Port]), Port},
+    validate_sys_mon_info(PidOrPort, SysMonName, ValidateInfo, InfoOrPort).
+
 t_sys_mon2(_Config) ->
     ?SYSMON ! {timeout, ignored, reset},
     ?SYSMON ! {ignored},
@@ -156,3 +166,8 @@ some_function(Parent, _Arg2) ->
         stop ->
             ok
     end.
+
+dead_port() ->
+    Port = erlang:open_port({spawn, "ls"}, []),
+    catch exit(Port, kill),
+    Port.

From 0e319d5e4e0b32e75e1cb53bbc11ac328e100524 Mon Sep 17 00:00:00 2001
From: Thales Macedo Garitezi <thalesmg@gmail.com>
Date: Thu, 24 Feb 2022 16:28:00 -0300
Subject: [PATCH 3/3] fix: rm useless `catch`

---
 apps/emqx/test/emqx_sys_mon_SUITE.erl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/apps/emqx/test/emqx_sys_mon_SUITE.erl b/apps/emqx/test/emqx_sys_mon_SUITE.erl
index c14074f0d..338188c21 100644
--- a/apps/emqx/test/emqx_sys_mon_SUITE.erl
+++ b/apps/emqx/test/emqx_sys_mon_SUITE.erl
@@ -169,5 +169,5 @@ some_function(Parent, _Arg2) ->
 
 dead_port() ->
     Port = erlang:open_port({spawn, "ls"}, []),
-    catch exit(Port, kill),
+    exit(Port, kill),
     Port.