We need no write barrier here; ref
MODIFY
src/vm.c
src/vm.c
@@ -1984,10 +1984,7 @@ RETRY_TRY_BLOCK:
while (c->eidx > ci->epos) {
ecall_adjust();
}
- if (c->fib) {
- mrb_write_barrier(mrb, (struct RBasic*)c->fib);
- }
- mrb->c->status = MRB_FIBER_TERMINATED;
+ c->status = MRB_FIBER_TERMINATED;
mrb->c = c->prev;
c->prev = NULL;
goto L_RAISE;

We need no write barrier here; ref #4143