6 files changed, 66 insertions, 81 deletions
diff --git a/ractor.c b/ractor.c
index 3eedf59048..cce376c543 100644
--- a/ractor.c
+++ b/ractor.c
@@ -1358,24 +1358,24 @@ make_shareable_check_shareable(VALUE obj)
     }
 
     switch (TYPE(obj)) {
-        case T_IMEMO:
-          return traverse_skip;
-        case T_OBJECT:
-          {
-              // If a T_OBJECT is shared and has no free capacity, we can't safely store the object_id inline,
-              // as it would require to move the object content into an external buffer.
-              // This is only a problem for T_OBJECT, given other types have external fields and can do RCU.
-              // To avoid this issue, we proactively create the object_id.
-              shape_id_t shape_id = RBASIC_SHAPE_ID(obj);
-              attr_index_t capacity = RSHAPE_CAPACITY(shape_id);
-              attr_index_t free_capacity = capacity - RSHAPE_LEN(shape_id);
-              if (!rb_shape_has_object_id(shape_id) && capacity && !free_capacity) {
-                  rb_obj_id(obj);
-              }
-          }
-          break;
-        default:
-          break;
+      case T_IMEMO:
+        return traverse_skip;
+      case T_OBJECT:
+        {
+            // If a T_OBJECT is shared and has no free capacity, we can't safely store the object_id inline,
+            // as it would require to move the object content into an external buffer.
+            // This is only a problem for T_OBJECT, given other types have external fields and can do RCU.
+            // To avoid this issue, we proactively create the object_id.
+            shape_id_t shape_id = RBASIC_SHAPE_ID(obj);
+            attr_index_t capacity = RSHAPE_CAPACITY(shape_id);
+            attr_index_t free_capacity = capacity - RSHAPE_LEN(shape_id);
+            if (!rb_shape_has_object_id(shape_id) && capacity && !free_capacity) {
+                rb_obj_id(obj);
+            }
+        }
+        break;
+      default:
+        break;
     }
 
     if (!RB_OBJ_FROZEN_RAW(obj)) {
diff --git a/spec/ruby/optional/capi/digest_spec.rb b/spec/ruby/optional/capi/digest_spec.rb
index c753733906..65c5ecebb1 100644
--- a/spec/ruby/optional/capi/digest_spec.rb
+++ b/spec/ruby/optional/capi/digest_spec.rb
@@ -1,6 +1,10 @@
 require_relative 'spec_helper'
 
-require 'fiddle'
+begin
+  require 'fiddle'
+rescue LoadError
+  return
+end
 
 load_extension('digest')
 
diff --git a/st.c b/st.c
index f11e9efaf9..70da7daf83 100644
--- a/st.c
+++ b/st.c
@@ -1495,7 +1495,16 @@ st_update(st_table *tab, st_data_t key,
         value = entry->record;
     }
     old_key = key;
+
+    unsigned int rebuilds_num = tab->rebuilds_num;
+
     retval = (*func)(&key, &value, arg, existing);
+
+    // We need to make sure that the callback didn't cause a table rebuild
+    // Ideally we would make sure no operations happened
+    assert(rebuilds_num == tab->rebuilds_num);
+    (void)rebuilds_num;
+
     switch (retval) {
       case ST_CONTINUE:
         if (! existing) {
diff --git a/test/ruby/test_object_id.rb b/test/ruby/test_object_id.rb
index 018cc81496..9c0099517b 100644
--- a/test/ruby/test_object_id.rb
+++ b/test/ruby/test_object_id.rb
@@ -243,35 +243,4 @@ class TestObjectIdRactor < Test::Unit::TestCase
       assert_equal object_id, obj.object_id
     end;
   end
-
-  def test_object_id_race_free_with_stress_compact
-    assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
-    begin;
-      Warning[:experimental] = false
-      class MyClass
-        attr_reader :a, :b, :c
-        def initialize
-          @a = @b = @c = nil
-        end
-      end
-      N = 20
-      objs = Ractor.make_shareable(N.times.map { MyClass.new })
-
-      GC.stress = true
-      GC.auto_compact = true if GC.respond_to?(:auto_compact=)
-
-      results = 4.times.map{
-        Ractor.new(objs) { |objs|
-          vars = []
-          ids = []
-          objs.each do |obj|
-            vars << obj.a << obj.b << obj.c
-            ids << obj.object_id
-          end
-          [vars, ids]
-        }
-      }.map(&:value)
-      assert_equal 1, results.uniq.size
-    end;
-  end
 end
diff --git a/test/ruby/test_variable.rb b/test/ruby/test_variable.rb
index 49fec2d40e..984045e05d 100644
--- a/test/ruby/test_variable.rb
+++ b/test/ruby/test_variable.rb
@@ -407,6 +407,20 @@ class TestVariable < Test::Unit::TestCase
     }
   end
 
+  def test_exivar_resize_with_compaction_stress
+    omit "compaction doesn't work well on s390x" if RUBY_PLATFORM =~ /s390x/ # https://github.com/ruby/ruby/pull/5077
+    objs = 10_000.times.map do
+      ExIvar.new
+    end
+    EnvUtil.under_gc_compact_stress do
+      10.times do
+        x = ExIvar.new
+        x.instance_variable_set(:@resize, 1)
+        x
+      end
+    end
+  end
+
   def test_local_variables_with_kwarg
     bug11674 = '[ruby-core:71437] [Bug #11674]'
     v = with_kwargs_11(v1:1,v2:2,v3:3,v4:4,v5:5,v6:6,v7:7,v8:8,v9:9,v10:10,v11:11)
diff --git a/variable.c b/variable.c
index 67dc2d3397..6bd9f69d06 100644
--- a/variable.c
+++ b/variable.c
@@ -1818,51 +1818,40 @@ general_field_set(VALUE obj, shape_id_t target_shape_id, VALUE val, void *data,
 struct gen_fields_lookup_ensure_size {
     VALUE obj;
     ID id;
-    struct gen_fields_tbl *fields_tbl;
     shape_id_t shape_id;
     bool resize;
 };
 
-static int
-generic_fields_lookup_ensure_size(st_data_t *k, st_data_t *v, st_data_t u, int existing)
-{
-    ASSERT_vm_locking();
-
-    struct gen_fields_lookup_ensure_size *fields_lookup = (struct gen_fields_lookup_ensure_size *)u;
-    struct gen_fields_tbl *fields_tbl = existing ? (struct gen_fields_tbl *)*v : NULL;
-
-    if (!existing || fields_lookup->resize) {
-        if (existing) {
-            RUBY_ASSERT(RSHAPE_TYPE_P(fields_lookup->shape_id, SHAPE_IVAR) || RSHAPE_TYPE_P(fields_lookup->shape_id, SHAPE_OBJ_ID));
-            RUBY_ASSERT(RSHAPE_CAPACITY(RSHAPE_PARENT(fields_lookup->shape_id)) < RSHAPE_CAPACITY(fields_lookup->shape_id));
-        }
-
-        fields_tbl = gen_fields_tbl_resize(fields_tbl, RSHAPE_CAPACITY(fields_lookup->shape_id));
-        *v = (st_data_t)fields_tbl;
-    }
-
-    fields_lookup->fields_tbl = fields_tbl;
-    if (fields_lookup->shape_id) {
-        rb_obj_set_shape_id(fields_lookup->obj, fields_lookup->shape_id);
-    }
-
-    RUBY_ASSERT(rb_obj_exivar_p((VALUE)*k));
-
-    return ST_CONTINUE;
-}
-
 static VALUE *
 generic_ivar_set_shape_fields(VALUE obj, void *data)
 {
     RUBY_ASSERT(!rb_shape_obj_too_complex_p(obj));
 
     struct gen_fields_lookup_ensure_size *fields_lookup = data;
+    struct gen_fields_tbl *fields_tbl = NULL;
 
+    // We can't use st_update, since when resizing the fields table GC can
+    // happen, which will modify the st_table and may rebuild it
     RB_VM_LOCKING() {
-        st_update(generic_fields_tbl(obj, fields_lookup->id, false), (st_data_t)obj, generic_fields_lookup_ensure_size, (st_data_t)fields_lookup);
+        st_table *tbl = generic_fields_tbl(obj, fields_lookup->id, false);
+        int existing = st_lookup(tbl, (st_data_t)obj, (st_data_t *)&fields_tbl);
+
+        if (!existing || fields_lookup->resize) {
+            if (existing) {
+                RUBY_ASSERT(RSHAPE_TYPE_P(fields_lookup->shape_id, SHAPE_IVAR) || RSHAPE_TYPE_P(fields_lookup->shape_id, SHAPE_OBJ_ID));
+                RUBY_ASSERT(RSHAPE_CAPACITY(RSHAPE_PARENT(fields_lookup->shape_id)) < RSHAPE_CAPACITY(fields_lookup->shape_id));
+            }
+
+            fields_tbl = gen_fields_tbl_resize(fields_tbl, RSHAPE_CAPACITY(fields_lookup->shape_id));
+            st_insert(tbl, (st_data_t)obj, (st_data_t)fields_tbl);
+        }
+
+        if (fields_lookup->shape_id) {
+            rb_obj_set_shape_id(fields_lookup->obj, fields_lookup->shape_id);
+        }
     }
 
-    return fields_lookup->fields_tbl->as.shape.fields;
+    return fields_tbl->as.shape.fields;
 }
 
 static void