From fa44f865c3fc6253cf4691cf94839c303a3ee40f Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Tue, 15 Dec 2015 20:32:39 +0100
Subject: erts: Make erlang:purge_module/1 safe

Problem: erlang:purge_module/1 is not safe in the sense
that very bad things may happen if the code to be purged
is still referred to by live processes.

Introduce erts_internal:purge_module which is the same as the old
erlang:purge_module BIF (except it returns false if no such old module).

Implement erlang:purge_module in Erlang and let it invoke
erts_code_purger for safe purging where all clogging processes
first are killed.
---
 erts/preloaded/ebin/erlang.beam           | Bin 102216 -> 102556 bytes
 erts/preloaded/ebin/erts_code_purger.beam | Bin 9020 -> 8992 bytes
 erts/preloaded/ebin/erts_internal.beam    | Bin 6260 -> 6432 bytes
 erts/preloaded/ebin/init.beam             | Bin 44700 -> 44728 bytes
 erts/preloaded/src/erlang.erl             |  12 ++++++++++--
 erts/preloaded/src/erts_code_purger.erl   |  14 +++-----------
 erts/preloaded/src/erts_internal.erl      |   6 ++++++
 erts/preloaded/src/init.erl               |   4 ++--
 8 files changed, 21 insertions(+), 15 deletions(-)

(limited to 'erts/preloaded')

diff --git a/erts/preloaded/ebin/erlang.beam b/erts/preloaded/ebin/erlang.beam
index 68578c3a49..4353e115ca 100644
Binary files a/erts/preloaded/ebin/erlang.beam and b/erts/preloaded/ebin/erlang.beam differ
diff --git a/erts/preloaded/ebin/erts_code_purger.beam b/erts/preloaded/ebin/erts_code_purger.beam
index adfe298a44..553b34b105 100644
Binary files a/erts/preloaded/ebin/erts_code_purger.beam and b/erts/preloaded/ebin/erts_code_purger.beam differ
diff --git a/erts/preloaded/ebin/erts_internal.beam b/erts/preloaded/ebin/erts_internal.beam
index 4e1cb7f8a0..150e76505d 100644
Binary files a/erts/preloaded/ebin/erts_internal.beam and b/erts/preloaded/ebin/erts_internal.beam differ
diff --git a/erts/preloaded/ebin/init.beam b/erts/preloaded/ebin/init.beam
index a44b022931..b6d1df7bbc 100644
Binary files a/erts/preloaded/ebin/init.beam and b/erts/preloaded/ebin/init.beam differ
diff --git a/erts/preloaded/src/erlang.erl b/erts/preloaded/src/erlang.erl
index d9dc9a1976..ab54d716cc 100644
--- a/erts/preloaded/src/erlang.erl
+++ b/erts/preloaded/src/erlang.erl
@@ -1471,8 +1471,16 @@ processes() ->
 %% purge_module/1
 -spec purge_module(Module) -> true when
       Module :: atom().
-purge_module(_Module) ->
-    erlang:nif_error(undefined).
+purge_module(Module) when erlang:is_atom(Module) ->
+    case erts_code_purger:purge(Module) of
+	{false, _} ->
+	    erlang:error(badarg, [Module]);
+	{true, _} ->
+	    true
+    end;
+purge_module(Arg) ->
+    erlang:error(badarg, [Arg]).
+
 
 %% put/2
 -spec put(Key, Val) -> term() when
diff --git a/erts/preloaded/src/erts_code_purger.erl b/erts/preloaded/src/erts_code_purger.erl
index 6bb6e4fcdc..880c86aad1 100644
--- a/erts/preloaded/src/erts_code_purger.erl
+++ b/erts/preloaded/src/erts_code_purger.erl
@@ -70,12 +70,8 @@ do_purge(Mod) ->
             true = erlang:copy_literals(Mod, true),
             DidKill = check_proc_code(erlang:processes(), Mod, true),
             true = erlang:copy_literals(Mod, false),
-            try
-                erlang:purge_module(Mod)
-            catch
-                _:_ -> ignore
-            end,
-            {true, DidKill}
+	    WasPurged = erts_internal:purge_module(Mod),
+            {WasPurged, DidKill}
     end.
 
 %% soft_purge(Module)
@@ -104,11 +100,7 @@ do_soft_purge(Mod) ->
 		    false;
 		true ->
                     true = erlang:copy_literals(Mod, false),
-		    try
-			erlang:purge_module(Mod)
-		    catch
-			_:_ -> ignore
-		    end,
+		    erts_internal:purge_module(Mod),
 		    true
 	    end
     end.
diff --git a/erts/preloaded/src/erts_internal.erl b/erts/preloaded/src/erts_internal.erl
index 426749264f..6e649e8395 100644
--- a/erts/preloaded/src/erts_internal.erl
+++ b/erts/preloaded/src/erts_internal.erl
@@ -38,6 +38,7 @@
 -export([request_system_task/3]).
 
 -export([check_process_code/2]).
+-export([purge_module/1]).
 
 -export([flush_monitor_messages/3]).
 
@@ -204,6 +205,11 @@ request_system_task(_Pid, _Prio, _Request) ->
 check_process_code(_Module, _OptionList) ->
     erlang:nif_error(undefined).
 
+-spec purge_module(Module) -> boolean() when
+      Module :: module().
+purge_module(_Module) ->
+    erlang:nif_error(undefined).
+
 %% term compare where integer() < float() = true
 
 -spec cmp_term(A,B) -> Result when
diff --git a/erts/preloaded/src/init.erl b/erts/preloaded/src/init.erl
index 383c4a1ec6..ed65c57c0d 100644
--- a/erts/preloaded/src/init.erl
+++ b/erts/preloaded/src/init.erl
@@ -636,9 +636,9 @@ unload(_) ->
     do_unload(sub([heart|erlang:pre_loaded()],erlang:loaded())).
 
 do_unload([M|Mods]) ->
-    catch erlang:purge_module(M),
+    catch erts_internal:purge_module(M),
     catch erlang:delete_module(M),
-    catch erlang:purge_module(M),
+    catch erts_internal:purge_module(M),
     do_unload(Mods);
 do_unload([]) ->
     purge_all_hipe_refs(),
-- 
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