From a29442701785463d0febf5b8cf217246e927bfae Mon Sep 17 00:00:00 2001
From: Jean Boussier <jean.boussier@gmail.com>
Date: Thu, 15 May 2025 13:43:44 +0200
Subject: [PATCH] Add missing lock to `rb_gc_impl_copy_finalizer`

---
 gc/default/default.c         |  2 ++
 gc/mmtk/mmtk.c               |  2 ++
 test/objspace/test_ractor.rb | 21 +++++++++++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/gc/default/default.c b/gc/default/default.c
index 7743164732..5c6c2a9417 100644
--- a/gc/default/default.c
+++ b/gc/default/default.c
@@ -2803,6 +2803,7 @@ rb_gc_impl_copy_finalizer(void *objspace_ptr, VALUE dest, VALUE obj)
 
     if (!FL_TEST(obj, FL_FINALIZE)) return;
 
+    int lev = rb_gc_vm_lock();
     if (RB_LIKELY(st_lookup(finalizer_table, obj, &data))) {
         table = (VALUE)data;
         st_insert(finalizer_table, dest, table);
@@ -2811,6 +2812,7 @@ rb_gc_impl_copy_finalizer(void *objspace_ptr, VALUE dest, VALUE obj)
     else {
         rb_bug("rb_gc_copy_finalizer: FL_FINALIZE set but not found in finalizer_table: %s", rb_obj_info(obj));
     }
+    rb_gc_vm_unlock(lev);
 }
 
 static VALUE
diff --git a/gc/mmtk/mmtk.c b/gc/mmtk/mmtk.c
index aec48df07a..09a8c0bc5c 100644
--- a/gc/mmtk/mmtk.c
+++ b/gc/mmtk/mmtk.c
@@ -983,6 +983,7 @@ rb_gc_impl_copy_finalizer(void *objspace_ptr, VALUE dest, VALUE obj)
 
     if (!FL_TEST(obj, FL_FINALIZE)) return;
 
+    int lev = rb_gc_vm_lock();
     if (RB_LIKELY(st_lookup(objspace->finalizer_table, obj, &data))) {
         table = (VALUE)data;
         st_insert(objspace->finalizer_table, dest, table);
@@ -991,6 +992,7 @@ rb_gc_impl_copy_finalizer(void *objspace_ptr, VALUE dest, VALUE obj)
     else {
         rb_bug("rb_gc_copy_finalizer: FL_FINALIZE set but not found in finalizer_table: %s", rb_obj_info(obj));
     }
+    rb_gc_vm_unlock(lev);
 }
 
 static int
diff --git a/test/objspace/test_ractor.rb b/test/objspace/test_ractor.rb
index c5bb656da6..1176a78b4b 100644
--- a/test/objspace/test_ractor.rb
+++ b/test/objspace/test_ractor.rb
@@ -33,4 +33,25 @@ class TestObjSpaceRactor < Test::Unit::TestCase
       ractors.each(&:take)
     RUBY
   end
+
+  def test_copy_finalizer
+    assert_ractor(<<~'RUBY', require: 'objspace')
+      def fin
+        ->(id) { }
+      end
+      OBJ = Object.new
+      ObjectSpace.define_finalizer(OBJ, fin)
+      OBJ.freeze
+
+      ractors = 5.times.map do
+        Ractor.new do
+          10_000.times do
+            OBJ.clone
+          end
+        end
+      end
+
+      ractors.each(&:take)
+    RUBY
+  end
 end