DualPI2 drops packets during dequeue but was using kfree_skb_reason()
directly, bypassing trace_qdisc_drop. Convert to qdisc_dequeue_drop()
and add QDISC_DROP_L4S_STEP_NON_ECN to the qdisc drop reason enum.

- Set TCQ_F_DEQUEUE_DROPS flag in dualpi2_init()
- Use enum qdisc_drop_reason in drop_and_retry()
- Replace kfree_skb_reason() with qdisc_dequeue_drop()

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202602061240.CRDtcOeX-lkp@intel.com/
Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>
---
 include/net/dropreason-core.h  |    6 ------
 include/net/dropreason-qdisc.h |    8 ++++++++
 net/sched/sch_dualpi2.c        |   12 ++++++------
 3 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index 3d8d284e05c8..5c8c2eb3d2c5 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -121,7 +121,6 @@
 	FN(CANFD_RX_INVALID_FRAME)	\
 	FN(CANXL_RX_INVALID_FRAME)	\
 	FN(PFMEMALLOC)	\
-	FN(DUALPI2_STEP_DROP)		\
 	FN(PSP_INPUT)			\
 	FN(PSP_OUTPUT)			\
 	FNe(MAX)
@@ -579,11 +578,6 @@ enum skb_drop_reason {
 	 * reached a path or socket not eligible for use of memory reserves
 	 */
 	SKB_DROP_REASON_PFMEMALLOC,
-	/**
-	 * @SKB_DROP_REASON_DUALPI2_STEP_DROP: dropped by the step drop
-	 * threshold of DualPI2 qdisc.
-	 */
-	SKB_DROP_REASON_DUALPI2_STEP_DROP,
 	/** @SKB_DROP_REASON_PSP_INPUT: PSP input checks failed */
 	SKB_DROP_REASON_PSP_INPUT,
 	/** @SKB_DROP_REASON_PSP_OUTPUT: PSP output checks failed */
diff --git a/include/net/dropreason-qdisc.h b/include/net/dropreason-qdisc.h
index 8661797193b1..c08ecce2d76b 100644
--- a/include/net/dropreason-qdisc.h
+++ b/include/net/dropreason-qdisc.h
@@ -14,6 +14,7 @@
 	FN(FLOOD_PROTECTION)		\
 	FN(BAND_LIMIT)			\
 	FN(HORIZON_LIMIT)		\
+	FN(L4S_STEP_NON_ECN)			\
 	FNe(MAX)
 
 #undef FN
@@ -94,6 +95,13 @@ enum qdisc_drop_reason {
 	 * Used by qdiscs with time-based scheduling (e.g., FQ).
 	 */
 	QDISC_DROP_HORIZON_LIMIT,
+	/**
+	 * @QDISC_DROP_L4S_STEP_NON_ECN: DualPI2 qdisc dropped a non-ECN-capable
+	 * packet because the L4S queue delay exceeded the step threshold.
+	 * Since the packet cannot be ECN-marked, it must be dropped to signal
+	 * congestion. See RFC 9332 for the DualQ Coupled AQM step mechanism.
+	 */
+	QDISC_DROP_L4S_STEP_NON_ECN,
 	/**
 	 * @QDISC_DROP_MAX: the maximum of qdisc drop reasons, which
 	 * shouldn't be used as a real 'reason' - only for tracing code gen
diff --git a/net/sched/sch_dualpi2.c b/net/sched/sch_dualpi2.c
index 0b6a38704a3b..fe6f5e889625 100644
--- a/net/sched/sch_dualpi2.c
+++ b/net/sched/sch_dualpi2.c
@@ -571,11 +571,11 @@ static int do_step_aqm(struct dualpi2_sched_data *q, struct sk_buff *skb,
 }
 
 static void drop_and_retry(struct dualpi2_sched_data *q, struct sk_buff *skb,
-			   struct Qdisc *sch, enum skb_drop_reason reason)
+			   struct Qdisc *sch, enum qdisc_drop_reason reason)
 {
 	++q->deferred_drops_cnt;
 	q->deferred_drops_len += qdisc_pkt_len(skb);
-	kfree_skb_reason(skb, reason);
+	qdisc_dequeue_drop(sch, skb, reason);
 	qdisc_qstats_drop(sch);
 }
 
@@ -590,15 +590,13 @@ static struct sk_buff *dualpi2_qdisc_dequeue(struct Qdisc *sch)
 
 	while ((skb = dequeue_packet(sch, q, &credit_change, now))) {
 		if (!q->drop_early && must_drop(sch, q, skb)) {
-			drop_and_retry(q, skb, sch,
-				       QDISC_DROP_CONGESTED);
+			drop_and_retry(q, skb, sch, QDISC_DROP_CONGESTED);
 			continue;
 		}
 
 		if (skb_in_l_queue(skb) && do_step_aqm(q, skb, now)) {
 			qdisc_qstats_drop(q->l_queue);
-			drop_and_retry(q, skb, sch,
-				       SKB_DROP_REASON_DUALPI2_STEP_DROP);
+			drop_and_retry(q, skb, sch, QDISC_DROP_L4S_STEP_NON_ECN);
 			continue;
 		}
 
@@ -915,6 +913,8 @@ static int dualpi2_init(struct Qdisc *sch, struct nlattr *opt,
 	struct dualpi2_sched_data *q = qdisc_priv(sch);
 	int err;
 
+	sch->flags |= TCQ_F_DEQUEUE_DROPS;
+
 	q->l_queue = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
 				       TC_H_MAKE(sch->handle, 1), extack);
 	if (!q->l_queue)