In the Linux kernel, the following vulnerability has been resolved:
sch_htb: make htb_qlen_notify() idempotent
htb_qlen_notify() always deactivates the HTB class and in fact could trigger a warning if it is already deactivated. Therefore, it is not idempotent and not friendly to its callers, like fq_codel_dequeue().
Let's make it idempotent to ease qdisc_tree_reduce_backlog() callers' life.