Make pre-loaded modules permanently sticky

Modules in the kernel, stdlib, and compiler applications are by
default "sticky", meaning that the code server will refuse to
re-load them.

The pre-loaded modules (those that are part of the run-time system
itself, such as 'erlang') are, however, not sticky. They used to be
sticky a long time ago when the pre-loaded modules were part of
the kernel application. Now they are part of the erts application.

Since re-loading a pre-loaded module can be catastrophic (especially
re-loading the 'erlang' module), the pre-loaded modules must be
sticky. Furthermore, it should not be allowed to unstick them.

The sticky_dir/1 test case in code_SUITE is never actually run and
is broken. Rewrite it.

1 files changed, 14 insertions, 2 deletions

diff --git a/lib/kernel/src/code_server.erl b/lib/kernel/src/code_server.erl
index f891cb61c4..dd06affd70 100644
--- a/lib/kernel/src/code_server.erl
+++ b/lib/kernel/src/code_server.erl
@@ -63,7 +63,10 @@ init(Ref, Parent, [Root,Mode0]) ->
     process_flag(trap_exit, true),
 
     Db = ets:new(code, [private]),
-    foreach(fun (M) -> ets:insert(Db, {M,preloaded}) end, erlang:pre_loaded()),
+    foreach(fun (M) ->
+		    %% Pre-loaded modules are always sticky.
+		    ets:insert(Db, [{M,preloaded},{{sticky,M},true}])
+	    end, erlang:pre_loaded()),
     ets:insert(Db, init:fetch_loaded()),
 
     Mode = 
@@ -1165,7 +1168,7 @@ stick_dir(Dir, Stick, St) ->
 		true ->
 		    foreach(fun (M) -> ets:insert(Db, {{sticky,M},true}) end, Mods);
 		false ->
-		    foreach(fun (M) -> ets:delete(Db, {sticky,M}) end, Mods)
+		    foreach(fun (M) -> do_unstick_mod(Db, M) end, Mods)
 	    end;
 	Error -> 
 	    Error
@@ -1177,6 +1180,15 @@ stick_mod(M, Stick, St) ->
 	true ->
 	    ets:insert(Db, {{sticky,M},true});
 	false ->
+	    do_unstick_mod(Db, M)
+    end.
+
+do_unstick_mod(Db, M) ->
+    case ets:lookup(Db, M) of
+	[{M,preloaded}] ->
+	    %% Never unstick pre-loaded modules.
+	    true;
+	_ ->
 	    ets:delete(Db, {sticky,M})
     end.