From 206110a2a8f5d14f8e462c81065673c1dae1c2ef Mon Sep 17 00:00:00 2001
From: Jean Boussier <jean.boussier@gmail.com>
Date: Tue, 3 Jun 2025 15:52:29 +0200
Subject: [PATCH] Add missing lock in `rb_ivar_defined`

If called on a class, we should acquire the lock.
---
 variable.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/variable.c b/variable.c
index bef25c147f..b87cdd7986 100644
--- a/variable.c
+++ b/variable.c
@@ -2125,12 +2125,11 @@ rb_obj_field_set(VALUE obj, shape_id_t target_shape_id, VALUE val)
     }
 }
 
-VALUE
-rb_ivar_defined(VALUE obj, ID id)
+static VALUE
+ivar_defined0(VALUE obj, ID id)
 {
     attr_index_t index;
 
-    if (SPECIAL_CONST_P(obj)) return Qfalse;
     if (rb_shape_obj_too_complex_p(obj)) {
         VALUE idx;
         st_table *table = NULL;
@@ -2164,6 +2163,26 @@ rb_ivar_defined(VALUE obj, ID id)
     }
 }
 
+VALUE
+rb_ivar_defined(VALUE obj, ID id)
+{
+    if (SPECIAL_CONST_P(obj)) return Qfalse;
+
+    VALUE defined;
+    switch (BUILTIN_TYPE(obj)) {
+      case T_CLASS:
+      case T_MODULE:
+        RB_VM_LOCKING() {
+            defined = ivar_defined0(obj, id);
+        }
+        break;
+      default:
+        defined = ivar_defined0(obj, id);
+        break;
+    }
+    return defined;
+}
+
 struct iv_itr_data {
     VALUE obj;
     struct gen_fields_tbl *fields_tbl;