File 0189-Fix-race-condition-in-proc_lib-stop-3-with-small-tim.patch of Package erlang

From 311eb1258b697ac316f300ccee48b9a1b95c496b Mon Sep 17 00:00:00 2001
From: juhlig <juhlig@hnc-agency.org>
Date: Fri, 21 May 2021 17:37:29 +0200
Subject: [PATCH] Fix race condition in proc_lib:stop/3 with small timeouts

Ensures that the terminate message is always sent to the
target process.
Removes the obsolete proxy process.
---
 lib/stdlib/src/proc_lib.erl        | 51 +++++++++++++++---------------
 lib/stdlib/test/proc_lib_SUITE.erl | 39 +++++++++++++++--------
 2 files changed, 51 insertions(+), 39 deletions(-)

diff --git a/lib/stdlib/src/proc_lib.erl b/lib/stdlib/src/proc_lib.erl
index 58e6faf950..3bd68646fe 100644
--- a/lib/stdlib/src/proc_lib.erl
+++ b/lib/stdlib/src/proc_lib.erl
@@ -1062,33 +1062,32 @@ stop(Process) ->
       Reason :: term(),
       Timeout :: timeout().
 stop(Process, Reason, Timeout) ->
-    {Pid, Mref} = erlang:spawn_monitor(do_stop(Process, Reason)),
+    Mref = erlang:monitor(process, Process),
+    T0 = erlang:monotonic_time(millisecond),
+    RemainingTimeout = try
+	sys:terminate(Process, Reason, Timeout)
+    of
+	ok when Timeout =:= infinity ->
+	    infinity;
+	ok ->
+	    Timeout - (((erlang:monotonic_time(microsecond) + 999) div 1000) - T0)
+    catch
+	exit:{noproc, {sys, terminate, _}} ->
+	    demonitor(Mref, [flush]),
+	    exit(noproc);
+	exit:{timeout, {sys, terminate, _}} ->
+	    demonitor(Mref, [flush]),
+	    exit(timeout);
+	exit:Reason1 ->
+	    demonitor(Mref, [flush]),
+	    exit(Reason1)
+    end,
     receive
 	{'DOWN', Mref, _, _, Reason} ->
 	    ok;
-	{'DOWN', Mref, _, _, {noproc,{sys,terminate,_}}} ->
-	    exit(noproc);
-	{'DOWN', Mref, _, _, CrashReason} ->
-	    exit(CrashReason)
-    after Timeout ->
-	    exit(Pid, kill),
-	    receive
-		{'DOWN', Mref, _, _, _} ->
-		    exit(timeout)
-	    end
-    end.
-
--spec do_stop(Process, Reason) -> Fun when
-      Process :: pid() | RegName | {RegName,node()},
-      RegName :: atom(),
-      Reason :: term(),
-      Fun :: fun(() -> no_return()).
-do_stop(Process, Reason) ->
-    fun() ->
-	    Mref = erlang:monitor(process, Process),
-	    ok = sys:terminate(Process, Reason, infinity),
-	    receive
-		{'DOWN', Mref, _, _, ExitReason} ->
-		    exit(ExitReason)
-	    end
+	{'DOWN', Mref, _, _, Reason2} ->
+	    exit(Reason2)
+    after RemainingTimeout ->
+	demonitor(Mref, [flush]),
+	exit(timeout)
     end.
diff --git a/lib/stdlib/test/proc_lib_SUITE.erl b/lib/stdlib/test/proc_lib_SUITE.erl
index b3673efb5a..33109e93ad 100644
--- a/lib/stdlib/test/proc_lib_SUITE.erl
+++ b/lib/stdlib/test/proc_lib_SUITE.erl
@@ -668,34 +668,47 @@ stop(_Config) ->
     Pid3 = proc_lib:spawn(HangProc),
     {'EXIT',timeout} = (catch proc_lib:stop(Pid3,normal,1000)),
 
+    %% Ensure that a termination message is always sent to the
+    %% target process and that it eventually terminates.
+    Pid4 = proc_lib:spawn(HangProc),
+    Ref4 = monitor(process, Pid4),
+    {'EXIT', timeout} = (catch proc_lib:stop(Pid4, normal, 0)),
+    ok = receive
+	{'DOWN', Ref4, process, _, _} ->
+	    ok;
+	M -> M
+    after 6000 ->
+	timeout
+    end,
+
     %% Success case with other reason than 'normal'
-    Pid4 = proc_lib:spawn(SysMsgProc),
-    ok = proc_lib:stop(Pid4,other_reason,infinity),
-    false = erlang:is_process_alive(Pid4),
+    Pid5 = proc_lib:spawn(SysMsgProc),
+    ok = proc_lib:stop(Pid5,other_reason,infinity),
+    false = erlang:is_process_alive(Pid5),
 
     %% System message is handled, but process dies with other reason
     %% than the given (in system_terminate/4 below)
-    Pid5 = proc_lib:spawn(SysMsgProc),
-    {'EXIT',{{badmatch,2},_Stacktrace}} = (catch proc_lib:stop(Pid5,crash,infinity)),
-    false = erlang:is_process_alive(Pid5),
+    Pid6 = proc_lib:spawn(SysMsgProc),
+    {'EXIT',{{badmatch,2},_Stacktrace}} = (catch proc_lib:stop(Pid6,crash,infinity)),
+    false = erlang:is_process_alive(Pid6),
 
     %% Local registered name
-    Pid6 = proc_lib:spawn(SysMsgProc),
-    register(to_stop,Pid6),
+    Pid7 = proc_lib:spawn(SysMsgProc),
+    register(to_stop,Pid7),
     ok = proc_lib:stop(to_stop),
     undefined = whereis(to_stop),
-    false = erlang:is_process_alive(Pid6),
+    false = erlang:is_process_alive(Pid7),
 
     %% Remote registered name
     {ok,Node} = test_server:start_node(proc_lib_SUITE_stop,slave,[]),
     Dir = filename:dirname(code:which(?MODULE)),
     rpc:call(Node,code,add_path,[Dir]),
-    Pid7 = spawn(Node,SysMsgProc),
-    true = rpc:call(Node,erlang,register,[to_stop,Pid7]),
-    Pid7 = rpc:call(Node,erlang,whereis,[to_stop]),
+    Pid8 = spawn(Node,SysMsgProc),
+    true = rpc:call(Node,erlang,register,[to_stop,Pid8]),
+    Pid8 = rpc:call(Node,erlang,whereis,[to_stop]),
     ok = proc_lib:stop({to_stop,Node}),
     undefined = rpc:call(Node,erlang,whereis,[to_stop]),
-    false = rpc:call(Node,erlang,is_process_alive,[Pid7]),
+    false = rpc:call(Node,erlang,is_process_alive,[Pid8]),
 
     %% Local and remote registered name, but non-existing
     {'EXIT',noproc} = (catch proc_lib:stop(to_stop)),
-- 
2.26.2