codel: remove sch->q.qlen check before qdisc_tree_reduce_backlog()

jira LE-3845
cve CVE-2025-38350
Rebuild_History Non-Buildable kernel-4.18.0-553.69.1.el8_10
commit-author Cong Wang <[email protected]>
commit 342debc

After making all ->qlen_notify() callbacks idempotent, now it is safe to
remove the check of qlen!=0 from both fq_codel_dequeue() and
codel_qdisc_dequeue().

	Reported-by: Gerrard Tai <[email protected]>
Fixes: 4b549a2 ("fq_codel: Fair Queue Codel AQM")
Fixes: 76e3cc1 ("codel: Controlled Delay AQM")
	Signed-off-by: Cong Wang <[email protected]>
	Reviewed-by: Simon Horman <[email protected]>
Link: https://patch.msgid.link/[email protected]
	Acked-by: Jamal Hadi Salim <[email protected]>
	Signed-off-by: Paolo Abeni <[email protected]>
(cherry picked from commit 342debc)
	Signed-off-by: Jonathan Maple <[email protected]>

Author: PlaidCat

net/sched/sch_codel.c

@@ -95,10 +95,7 @@ static struct sk_buff *codel_qdisc_dequeue(struct Qdisc *sch)
 			    &q->stats, qdisc_pkt_len, codel_get_enqueue_time,
 			    drop_func, dequeue_func);
 
-	/* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
-	 * or HTB crashes. Defer it for next round.
-	 */
-	if (q->stats.drop_count && sch->q.qlen) {
+	if (q->stats.drop_count) {
 		qdisc_tree_reduce_backlog(sch, q->stats.drop_count, q->stats.drop_len);
 		q->stats.drop_count = 0;
 		q->stats.drop_len = 0;

net/sched/sch_fq_codel.c

@@ -318,10 +318,8 @@ static struct sk_buff *fq_codel_dequeue(struct Qdisc *sch)
 	}
 	qdisc_bstats_update(sch, skb);
 	flow->deficit -= qdisc_pkt_len(skb);
-	/* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
-	 * or HTB crashes. Defer it for next round.
-	 */
-	if (q->cstats.drop_count && sch->q.qlen) {
+
+	if (q->cstats.drop_count) {
 		qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
 					  q->cstats.drop_len);
 		q->cstats.drop_count = 0;