Create new enum qdisc_drop_reason and trace_qdisc_drop tracepoint
for qdisc layer drop diagnostics with direct qdisc context visibility.

The new tracepoint includes qdisc handle, parent, kind (name), and
device information. Existing SKB_DROP_REASON_QDISC_DROP is retained
for backwards compatibility via kfree_skb_reason().

Convert FQ, FQ_CoDel, CoDel, SFB, and pfifo_fast to use the new
infrastructure.

Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>
---
 include/net/dropreason-core.h  |   42 ++----------------
 include/net/dropreason-qdisc.h |   94 ++++++++++++++++++++++++++++++++++++++++
 include/net/dropreason.h       |    6 +++
 include/net/sch_generic.h      |   36 ++++++++++-----
 include/trace/events/qdisc.h   |   51 ++++++++++++++++++++++
 net/core/dev.c                 |    8 ++-
 net/sched/sch_cake.c           |    6 +--
 net/sched/sch_codel.c          |    5 +-
 net/sched/sch_dualpi2.c        |    8 +--
 net/sched/sch_fq.c             |    7 +--
 net/sched/sch_fq_codel.c       |    4 +-
 net/sched/sch_fq_pie.c         |    4 +-
 net/sched/sch_generic.c        |   22 +++++++++
 net/sched/sch_gred.c           |    4 +-
 net/sched/sch_pie.c            |    4 +-
 net/sched/sch_red.c            |    4 +-
 net/sched/sch_sfb.c            |    4 +-
 17 files changed, 225 insertions(+), 84 deletions(-)
 create mode 100644 include/net/dropreason-qdisc.h

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index a7b7abd66e21..3d8d284e05c8 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h

@@ -68,12 +68,6 @@
 	FN(SECURITY_HOOK)		\
 	FN(QDISC_DROP)			\
 	FN(QDISC_BURST_DROP)		\
-	FN(QDISC_OVERLIMIT)		\
-	FN(QDISC_CONGESTED)		\
-	FN(CAKE_FLOOD)			\
-	FN(FQ_BAND_LIMIT)		\
-	FN(FQ_HORIZON_LIMIT)		\
-	FN(FQ_FLOW_LIMIT)		\
 	FN(CPU_BACKLOG)			\
 	FN(XDP)				\
 	FN(TC_INGRESS)			\

@@ -371,8 +365,10 @@ enum skb_drop_reason {
 	/** @SKB_DROP_REASON_SECURITY_HOOK: dropped due to security HOOK */
 	SKB_DROP_REASON_SECURITY_HOOK,
 	/**
-	 * @SKB_DROP_REASON_QDISC_DROP: dropped by qdisc when packet outputting (
-	 * failed to enqueue to current qdisc)
+	 * @SKB_DROP_REASON_QDISC_DROP: dropped by qdisc during enqueue or
+	 * dequeue. More specific drop reasons are available via the
+	 * qdisc:qdisc_drop tracepoint, which also provides qdisc handle
+	 * and name for identifying the source.

@@ -37,6 +37,24 @@
 const struct Qdisc_ops *default_qdisc_ops = &pfifo_fast_ops;
 EXPORT_SYMBOL(default_qdisc_ops);
 
+void tcf_kfree_skb_list(struct sk_buff *skb, struct Qdisc *q,
+			struct netdev_queue *txq,
+			struct net_device *dev)
+{
+	while (unlikely(skb)) {
+		struct sk_buff *next = skb->next;
+		enum qdisc_drop_reason reason = tcf_get_qdisc_drop_reason(skb);
+
+		prefetch(next);
+		/* Catch wrong enum: skb_drop_reason vs qdisc_drop_reason */
+		WARN_ON_ONCE(reason && reason < __QDISC_DROP_REASON);
+		trace_qdisc_drop(q, txq, dev, skb, reason);
+		kfree_skb_reason(skb, SKB_DROP_REASON_QDISC_DROP);