https://git.ruby-lang.org/ruby.git/commit/?id=1a9dd31910

From 1a9dd31910699c7cd69f2a84c94af20eacd5875c Mon Sep 17 00:00:00 2001
From: Aaron Patterson <tenderlove@r...>
Date: Fri, 18 Sep 2020 10:50:27 -0700
Subject: Pin values in the finalizer table

When finalizers run (in `rb_objspace_call_finalizer`) the table is
copied to a linked list that is not managed by the GC.  If compaction
runs, the references in the linked list can go bad.

Finalizer table shouldn't be used frequently, so lets pin references in
the table so that the linked list in `rb_objspace_call_finalizer` is
safe.

diff --git a/gc.c b/gc.c
index 4b0fd06..eff5486 100644
--- a/gc.c
+++ b/gc.c
@@ -5046,11 +5046,19 @@ mark_set(rb_objspace_t *objspace, st_table *tbl) https://github.com/ruby/ruby/blob/trunk/gc.c#L5046
     st_foreach(tbl, mark_key, (st_data_t)objspace);
 }
 
+static int
+pin_value(st_data_t key, st_data_t value, st_data_t data)
+{
+    rb_objspace_t *objspace = (rb_objspace_t *)data;
+    gc_mark_and_pin(objspace, (VALUE)value);
+    return ST_CONTINUE;
+}
+
 static void
 mark_finalizer_tbl(rb_objspace_t *objspace, st_table *tbl)
 {
     if (!tbl) return;
-    st_foreach(tbl, mark_value, (st_data_t)objspace);
+    st_foreach(tbl, pin_value, (st_data_t)objspace);
 }
 
 void
@@ -7846,11 +7854,6 @@ gc_is_moveable_obj(rb_objspace_t *objspace, VALUE obj) https://github.com/ruby/ruby/blob/trunk/gc.c#L7854
       case T_RATIONAL:
       case T_NODE:
       case T_CLASS:
-        if (FL_TEST(obj, FL_FINALIZE)) {
-            if (st_is_member(finalizer_table, obj)) {
-                return FALSE;
-            }
-        }
         return RVALUE_MARKED(obj) && !RVALUE_PINNED(obj);
 
       default:
@@ -8748,7 +8751,6 @@ gc_update_references(rb_objspace_t * objspace) https://github.com/ruby/ruby/blob/trunk/gc.c#L8751
     gc_update_tbl_refs(objspace, objspace->obj_to_id_tbl);
     gc_update_table_refs(objspace, objspace->id_to_obj_tbl);
     gc_update_table_refs(objspace, global_symbols.str_sym);
-    gc_update_table_refs(objspace, finalizer_table);
 }
 
 static VALUE type_sym(size_t type);
-- 
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