From ff198ad904652ddea3af0a976867ae2c2b6cf5b8 Mon Sep 17 00:00:00 2001
From: Luke Gruber <luke.gruber@shopify.com>
Date: Fri, 3 Oct 2025 12:25:20 -0400
Subject: [PATCH] Add assertion to rb_gc_impl_writebarrier

We should only be executing WBs when GC is not running. We ran into this
issue when debugging 3cd2407045a67838cf2ab949e5164676b6870958.
---
 gc/default/default.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/gc/default/default.c b/gc/default/default.c
index 9b40fed097..c23adae062 100644
--- a/gc/default/default.c
+++ b/gc/default/default.c
@@ -6044,6 +6044,7 @@ rb_gc_impl_writebarrier(void *objspace_ptr, VALUE a, VALUE b)
 
     if (SPECIAL_CONST_P(b)) return;
 
+    GC_ASSERT(!during_gc);
     GC_ASSERT(RB_BUILTIN_TYPE(a) != T_NONE);
     GC_ASSERT(RB_BUILTIN_TYPE(a) != T_MOVED);
     GC_ASSERT(RB_BUILTIN_TYPE(a) != T_ZOMBIE);