Don't leak old code when loading a modules with an on_load function

Normally, calling code:delete/1 before re-loading the code for a
module is unnecessary but causes no problem.

But there will be be problems if the new code has an on_load function.
Code with an on_load function will always be loaded as old code
to allowed it to be easily purged if the on_load function would fail.
If the on_load function succeeds, the old and current code will be
swapped.

So in the scenario where code:delete/1 has been called explicitly,
there is old code but no current code. Loading code with an
on_load function will cause the reference to the old code to be
overwritten. That will at best cause a memory leak, and at worst
an emulator crash (especially if NIFs are involved).

To avoid that situation, we will put the code with the on_load
function in a special, third slot in Module.

ERL-240

1 files changed, 1 insertions, 2 deletions

diff --git a/lib/kernel/src/code_server.erl b/lib/kernel/src/code_server.erl
index 48541ec500..38c1169308 100644
--- a/lib/kernel/src/code_server.erl
+++ b/lib/kernel/src/code_server.erl
@@ -1382,11 +1382,10 @@ finish_on_load(PidRef, OnLoadRes, #state{on_load=OnLoad0}=St0) ->
 
 finish_on_load_1(Mod, OnLoadRes, Waiting, St) ->
     Keep = OnLoadRes =:= ok,
-    erlang:finish_after_on_load(Mod, Keep),
+    erts_code_purger:finish_after_on_load(Mod, Keep),
     Res = case Keep of
 	      false ->
 		  _ = finish_on_load_report(Mod, OnLoadRes),
-		  _ = erts_code_purger:purge(Mod),
 		  {error,on_load_failure};
 	      true ->
 		  {module,Mod}