Merge branch 'net_sched-fix-a-regression-in-sch_htb'

Cong Wang says:

====================
net_sched: fix a regression in sch_htb

This patchset contains a fix for the regression reported by Alan and a
selftest to cover that case. Please see each patch description for more
details.
====================

Link: https://patch.msgid.link/20250428232955.1740419-1-xiyou.wangcong@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

net/sched/sch_htb.c

@@ -348,7 +348,8 @@ static void htb_add_to_wait_tree(struct htb_sched *q,
  */
 static inline void htb_next_rb_node(struct rb_node **n)
 {
-	*n = rb_next(*n);
+	if (*n)
+		*n = rb_next(*n);
 }
 
 /**
@@ -609,8 +610,8 @@ static inline void htb_activate(struct htb_sched *q, struct htb_class *cl)
  */
 static inline void htb_deactivate(struct htb_sched *q, struct htb_class *cl)
 {
-	WARN_ON(!cl->prio_activity);
-
+	if (!cl->prio_activity)
+		return;
 	htb_deactivate_prios(q, cl);
 	cl->prio_activity = 0;
 }
@@ -1485,8 +1486,6 @@ static void htb_qlen_notify(struct Qdisc *sch, unsigned long arg)
 {
 	struct htb_class *cl = (struct htb_class *)arg;
 
-	if (!cl->prio_activity)
-		return;
 	htb_deactivate(qdisc_priv(sch), cl);
 }
 
@@ -1740,8 +1739,7 @@ static int htb_delete(struct Qdisc *sch, unsigned long arg,
 	if (cl->parent)
 		cl->parent->children--;
 
-	if (cl->prio_activity)
-		htb_deactivate(q, cl);
+	htb_deactivate(q, cl);
 
 	if (cl->cmode != HTB_CAN_SEND)
 		htb_safe_rb_erase(&cl->pq_node,
@@ -1949,8 +1947,7 @@ static int htb_change_class(struct Qdisc *sch, u32 classid,
 			/* turn parent into inner node */
 			qdisc_purge_queue(parent->leaf.q);
 			parent_qdisc = parent->leaf.q;
-			if (parent->prio_activity)
-				htb_deactivate(q, parent);
+			htb_deactivate(q, parent);
 
 			/* remove from evt list because of level change */
 			if (parent->cmode != HTB_CAN_SEND) {

tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json

@@ -538,5 +538,40 @@
             "$TC qdisc del dev $DUMMY handle 1:0 root",
             "$IP addr del 10.10.10.10/24 dev $DUMMY || true"
         ]
+    },
+    {
+        "id": "62c4",
+        "name": "Test HTB with FQ_CODEL - basic functionality",
+        "category": [
+            "qdisc",
+            "htb",
+            "fq_codel"
+        ],
+        "plugins": {
+            "requires": [
+                "nsPlugin",
+                "scapyPlugin"
+            ]
+        },
+        "setup": [
+            "$TC qdisc add dev $DEV1 root handle 1: htb default 11",
+            "$TC class add dev $DEV1 parent 1: classid 1:1 htb rate 10kbit",
+            "$TC class add dev $DEV1 parent 1:1 classid 1:11 htb rate 10kbit prio 0 quantum 1486",
+            "$TC qdisc add dev $DEV1 parent 1:11 fq_codel quantum 300 noecn",
+            "sleep 0.5"
+        ],
+        "scapy": {
+            "iface": "$DEV0",
+            "count": 5,
+            "packet": "Ether()/IP(dst='10.10.10.1', src='10.10.10.10')/TCP(sport=12345, dport=80)"
+        },
+        "cmdUnderTest": "$TC -s qdisc show dev $DEV1",
+        "expExitCode": "0",
+        "verifyCmd": "$TC -s qdisc show dev $DEV1 | grep -A 5 'qdisc fq_codel'",
+        "matchPattern": "Sent [0-9]+ bytes [0-9]+ pkt",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DEV1 handle 1: root"
+        ]
     }
 ]