File 0472-Fix-hanging-gen_tcp-send-vs-close-race.patch of Package erlang

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File 0472-Fix-hanging-gen_tcp-send-vs-close-race.patch of Package erlang (Revision 84136f040b8e10a77a20fc548a9bd409)

Currently displaying revision 84136f040b8e10a77a20fc548a9bd409 , Show latest

From 1292f8c229a7bf233b84660baea8ee9612515510 Mon Sep 17 00:00:00 2001
From: Raimo Niskanen <raimo@erlang.org>
Date: Thu, 11 Oct 2018 16:47:50 +0200
Subject: [PATCH 1/2] Fix hanging gen_tcp send vs close race

While a gen_tcp send was in progress with filled buffers
and slow receiver a close (from another process) would place
the port in a half dead state so the port could not signal
back to send, that waited for confirmation.

The solution is to after some time (5 s) of waiting for
send confirmation set a monitor on the port, which detects
if the port becomes half dead due to close from another process.

The close pending loop has also been improved to use the linger
timeout for waiting, and to set a system timeout (arbitrarily
selected 3 min) to not wait forever when the other end
reads data s l o w l y (tarpitting, kind of).
---
 erts/preloaded/ebin/prim_inet.beam | Bin 79028 -> 80628 bytes
 erts/preloaded/src/prim_inet.erl   | 143 ++++++++++++++++++++++++++++++-------
 2 files changed, 116 insertions(+), 27 deletions(-)

diff --git a/erts/preloaded/src/prim_inet.erl b/erts/preloaded/src/prim_inet.erl
index 8169943dde..5c2819032f 100644
--- a/erts/preloaded/src/prim_inet.erl
+++ b/erts/preloaded/src/prim_inet.erl
@@ -49,9 +49,15 @@
 -include("inet_sctp.hrl").
 -include("inet_int.hrl").
 
-%-define(DEBUG, 1).
+%%%-define(DEBUG, 1).
 -ifdef(DEBUG).
--define(DBG_FORMAT(Format, Args), (io:format((Format), (Args)))).
+-define(
+   DBG_FORMAT(Format, Args),
+   begin
+       %% io:format((Format), (Args)),
+       erlang:display(lists:flatten(io_lib:format((Format), (Args)))),
+       ok
+   end).
 -else.
 -define(DBG_FORMAT(Format, Args), ok).
 -endif.
@@ -150,39 +156,96 @@ shutdown_1(S, How) ->
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
 close(S) when is_port(S) ->
+    ?DBG_FORMAT("prim_inet:close(~p)~n", [S]),
     case getopt(S, linger) of
     	{ok,{true,0}} -> 
 	    close_port(S);
-	_ ->
-	    case subscribe(S, [subs_empty_out_q]) of
-		{ok, [{subs_empty_out_q,N}]} when N > 0 ->
-		    close_pend_loop(S, N);   %% wait for pending output to be sent
-		_ ->
-		    close_port(S)
-	    end
+        {ok,{true,T}} ->
+            %% Wait for T seconds for pending output to be sent
+            %%
+            %% Note that this handling of Linger may look ok,
+            %% but sweeps some problems under the rug since
+            %% there are OS buffers that may have remaining data
+            %% after the inet driver has emptied its buffers.
+            %% But Linger for nonblocking sockets is broken
+            %% anyway on all OS:es, according to hearsay,
+            %% and is a contradiction in itself.
+            %% We have hereby done our best...
+            %%
+            Tref = erlang:start_timer(T * 1000, self(), close_port),
+            close_pend_loop(S, Tref, undefined);
+	_ -> % Regard this as {ok,{false,_}}
+            case subscribe(S, [subs_empty_out_q]) of
+                {ok, [{subs_empty_out_q,N}]} when N > 0 ->
+                    %% Wait for pending output to be sent
+                    DefaultT = 180000, % Arbitrary system timeout 3 min
+                    Tref = erlang:start_timer(DefaultT, self(), close_port),
+                    close_pend_loop(S, Tref, N);
+                _ ->
+                    %% Subscribe failed or empty out q - give up or done
+                    close_port(S)
+            end
     end.
 
-close_pend_loop(S, N) ->
+close_pend_loop(S, Tref, N) ->
+    ?DBG_FORMAT("prim_inet:close_pend_loop(~p, _, ~p)~n", [S,N]),
     receive
-	{empty_out_q,S} ->
-	    close_port(S)
+        {timeout,Tref,_} -> % Linger timeout
+            ?DBG_FORMAT("prim_inet:close_pend_loop(~p, _, _) timeout~n", [S]),
+	    close_port(S);
+	{empty_out_q,S} when N =/= undefined ->
+            ?DBG_FORMAT(
+               "prim_inet:close_pend_loop(~p, _, _) empty_out_q~n", [S]),
+	    close_port(S, Tref)
     after ?INET_CLOSE_TIMEOUT ->
 	    case getstat(S, [send_pend]) of
                 {ok, [{send_pend,N1}]} ->
+                    ?DBG_FORMAT(
+                       "prim_inet:close_pend_loop(~p, _, _) send_pend ~p~n",
+                       [S,N1]),
                     if
-			N1 =:= N ->
-			    close_port(S);
-                       true ->
-			    close_pend_loop(S, N1)
+                        N1 =:= 0 ->
+                            %% Empty outq - done
+                            close_port(S, Tref);
+                        N =:= undefined ->
+                            %% Within linger time - wait some more
+                            close_pend_loop(S, Tref, N);
+                        N1 =:= N ->
+                            %% Inactivity - give up
+                            close_port(S, Tref);
+                        true ->
+                            %% Still moving - wait some more
+                            close_pend_loop(S, Tref, N)
                     end;
-		_ ->
-		    close_port(S)
-	    end
+                _Stat ->
+                    %% Failed getstat - give up
+                    ?DBG_FORMAT(
+                       "prim_inet:close_pend_loop(~p, _, _) getstat ~p~n",
+                       [S,_Stat]),
+		    close_port(S, Tref)
+            end
     end.
 
+
+close_port(S, Tref) ->
+    ?DBG_FORMAT("prim_inet:close_port(~p, _)~n", [S]),
+    case erlang:cancel_timer(Tref) of
+        false ->
+            receive
+                {timeout,Tref,_} ->
+                    ok
+            end;
+        _N ->
+            ok
+    end,
+    close_port(S).
+%%
 close_port(S) ->
-    catch erlang:port_close(S),
-    receive {'EXIT',S,_} -> ok after 0 -> ok end.
+    ?DBG_FORMAT("prim_inet:close_port(~p)~n", [S]),
+    _Closed = (catch erlang:port_close(S)),
+    receive {'EXIT',S,_} -> ok after 0 -> ok end,
+    ?DBG_FORMAT("prim_inet:close_port(~p) ~p~n", [S,_Closed]),
+    ok.
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%
@@ -424,23 +487,49 @@ peeloff(S, AssocId) ->
 %% be called directly -- use "sendmsg" instead:
 %%
 send(S, Data, OptList) when is_port(S), is_list(OptList) ->
-    ?DBG_FORMAT("prim_inet:send(~p, ~p)~n", [S,Data]),
+    ?DBG_FORMAT("prim_inet:send(~p, _, ~p)~n", [S,OptList]),
     try erlang:port_command(S, Data, OptList) of
 	false -> % Port busy and nosuspend option passed
 	    ?DBG_FORMAT("prim_inet:send() -> {error,busy}~n", []),
 	    {error,busy};
 	true ->
-	    receive
-		{inet_reply,S,Status} ->
-		    ?DBG_FORMAT("prim_inet:send() -> ~p~n", [Status]),
-		    Status
-	    end
+            send_recv_reply(S, undefined)
     catch
 	error:_Error ->
 	    ?DBG_FORMAT("prim_inet:send() -> {error,einval}~n", []),
 	     {error,einval}
     end.
 
+send_recv_reply(S, Mref) ->
+    ReplyTimeout =
+        case Mref of
+            undefined ->
+                ?INET_CLOSE_TIMEOUT;
+            _ ->
+                infinity
+        end,
+    receive
+        {inet_reply,S,Status} ->
+            ?DBG_FORMAT(
+               "prim_inet:send_recv_reply(~p, _): inet_reply ~p~n",
+               [S,Status]),
+            case Mref of
+                undefined -> ok;
+                _ ->
+                    demonitor(Mref, [flush]),
+                    ok
+            end,
+            Status;
+        {'DOWN',Mref,_,_,_Reason} when Mref =/= undefined ->
+            ?DBG_FORMAT(
+               "prim_inet:send_recv_reply(~p, _) 'DOWN' ~p~n",
+               [S,_Reason]),
+            {error,closed}
+    after ReplyTimeout ->
+            send_recv_reply(S, monitor(port, S))
+    end.
+
+
 send(S, Data) ->
     send(S, Data, []).
 
-- 
2.16.4

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File 0472-Fix-hanging-gen_tcp-send-vs-close-race.patch of Package erlang (Revision 84136f040b8e10a77a20fc548a9bd409)

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