GNU bug report logs - #27587
25.1; in the dynamic modules api, env->free_global_ref doesn't free anything

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Valentin Gatien-Baron <vgatien-baron <at> janestreet.com>
Subject: bug#27587: closed (Re: bug#27587: 25.1; in the dynamic modules
 api, env->free_global_ref doesn't free anything)
Date: Sun, 09 Jul 2017 22:18:02 +0000

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Your bug report

#27587: 25.1; in the dynamic modules api, env->free_global_ref doesn't free anything

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 27587 <at> debbugs.gnu.org.

-- 
27587: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=27587
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Philipp Stephani <p.stephani2 <at> gmail.com>
To: Valentin Gatien-Baron <vgatien-baron <at> janestreet.com>,
 27587-done <at> debbugs.gnu.org
Subject: Re: bug#27587: 25.1; in the dynamic modules api, env->free_global_ref
 doesn't free anything
Date: Sun, 09 Jul 2017 22:17:17 +0000

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Valentin Gatien-Baron <vgatien-baron <at> janestreet.com> schrieb am Mi., 5.
Juli 2017 um 17:07 Uhr:

> The following dynamic module takes unbounded memory:
>
> /* gcc -I . -g -ggdb -fPIC foo.c -shared -o foo.so && echo running &&
> emacs -Q -L . -batch -l foo */
> #include <emacs-module.h>
>
> int plugin_is_GPL_compatible;
>
> int emacs_module_init(struct emacs_runtime *ert) {
>   emacs_env *env = ert->get_environment(ert);
>   while (1) {
>     int i;
>     for (i = 0; i < 10000; i++) {
>       emacs_value v = env->make_string(env, "asdads", 3);
>       env->free_global_ref(env, env->make_global_ref(env, v));
>     }
>     env->funcall(env, env->intern(env, "garbage-collect"), 0, NULL);
>   }
> }
>
>
> This is because env->make_global_ref/env->free_global_ref leak memory.
> env->free_global_ref fails to remove values from the hash table of
> refcounts. The following patch makes the program above run in constant
> space.
>
>
> --- src/emacs-module.c 2017-06-30 16:00:36.776301646 -0400
> +++ src/emacs-module.c 2017-06-30 16:05:01.660120043 -0400
> @@ -308,7 +308,7 @@
>            set_hash_value_slot (h, i, value);
>          }
>        else
> - hash_remove_from_table (h, value);
> + hash_remove_from_table (h, obj);
>      }
>  }
>
>
Good catch, installed as 22af69906cca871fdb893e06d6f10dbbab4518e6.

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From: Valentin Gatien-Baron <vgatien-baron <at> janestreet.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.1; in the dynamic modules api, env->free_global_ref doesn't free
 anything
Date: Wed, 5 Jul 2017 08:43:26 -0400

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The following dynamic module takes unbounded memory:

/* gcc -I . -g -ggdb -fPIC foo.c -shared -o foo.so && echo running && emacs
-Q -L . -batch -l foo */
#include <emacs-module.h>

int plugin_is_GPL_compatible;

int emacs_module_init(struct emacs_runtime *ert) {
  emacs_env *env = ert->get_environment(ert);
  while (1) {
    int i;
    for (i = 0; i < 10000; i++) {
      emacs_value v = env->make_string(env, "asdads", 3);
      env->free_global_ref(env, env->make_global_ref(env, v));
    }
    env->funcall(env, env->intern(env, "garbage-collect"), 0, NULL);
  }
}


This is because env->make_global_ref/env->free_global_ref leak memory.
env->free_global_ref fails to remove values from the hash table of
refcounts. The following patch makes the program above run in constant
space.


--- src/emacs-module.c 2017-06-30 16:00:36.776301646 -0400
+++ src/emacs-module.c 2017-06-30 16:05:01.660120043 -0400
@@ -308,7 +308,7 @@
           set_hash_value_slot (h, i, value);
         }
       else
- hash_remove_from_table (h, value);
+ hash_remove_from_table (h, obj);
     }
 }

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