The logic for concurrent stack processing scans frames until a frame that supports stack watermark barriers is detected. They are detected on an opt-in basis. When this code was integrated in the JDK 17 time frame, there was no Graal support. So C1 frames and C2 frames opted in to this. However, today we still don't recognize JVMCI frames even though it's at least supposed to work for Graal. The implication is that we don't actually use this support for Graal frames.