In the Linux kernel, the following vulnerability has been resolved: schhfsc: make hfscqlennotify() idempotent hfscqlennotify() is not idempotent either and not friendly to its callers, like fqcodeldequeue(). Let's make it idempotent to ease qdisctreereducebacklog() callers' life: 1. updatevf() decreases cl->clnactive, so we can check whether it is non-zero before calling it. 2. eltreeremove() always removes RB node cl->elnode, but we can use RBEMPTYNODE() + RBCLEARNODE() to make it safe.