net: sched: Make tc-related drop reason more flexible for remaining qdiscs

Incrementing on Daniel's patch[1], make tc-related drop reason more
flexible for remaining qdiscs - that is, all qdiscs aside from clsact.
In essence, the drop reason will be set by cls_api and act_api in case
any error occurred in the data path. With that, we can give the user more
detailed information so that they can distinguish between a policy drop
or an error drop.

[1] https://lore.kernel.org/all/20231009092655.22025-1-daniel@iogearbox.netSigned-off-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/pkt_cls.h

@@ -154,22 +154,6 @@ __cls_set_class(unsigned long *clp, unsigned long cl)
 	return xchg(clp, cl);
 }
 
-struct tc_skb_cb;
-
-static inline struct tc_skb_cb *tc_skb_cb(const struct sk_buff *skb);
-
-static inline enum skb_drop_reason
-tcf_get_drop_reason(const struct sk_buff *skb)
-{
-	return tc_skb_cb(skb)->drop_reason;
-}
-
-static inline void tcf_set_drop_reason(const struct sk_buff *skb,
-				       enum skb_drop_reason reason)
-{
-	tc_skb_cb(skb)->drop_reason = reason;
-}
-
 static inline void
 __tcf_bind_filter(struct Qdisc *q, struct tcf_result *r, unsigned long base)
 {

include/net/pkt_sched.h

@@ -275,25 +275,6 @@ static inline void skb_txtime_consumed(struct sk_buff *skb)
 	skb->tstamp = ktime_set(0, 0);
 }
 
-struct tc_skb_cb {
-	struct qdisc_skb_cb qdisc_cb;
-	u32 drop_reason;
-
-	u16 zone; /* Only valid if post_ct = true */
-	u16 mru;
-	u8 post_ct:1;
-	u8 post_ct_snat:1;
-	u8 post_ct_dnat:1;
-};
-
-static inline struct tc_skb_cb *tc_skb_cb(const struct sk_buff *skb)
-{
-	struct tc_skb_cb *cb = (struct tc_skb_cb *)skb->cb;
-
-	BUILD_BUG_ON(sizeof(*cb) > sizeof_field(struct sk_buff, cb));
-	return cb;
-}
-
 static inline bool tc_qdisc_stats_dump(struct Qdisc *sch,
 				       unsigned long cl,
 				       struct qdisc_walker *arg)

include/net/sch_generic.h

@@ -1036,6 +1036,37 @@ static inline struct sk_buff *qdisc_dequeue_head(struct Qdisc *sch)
 	return skb;
 }
 
+struct tc_skb_cb {
+	struct qdisc_skb_cb qdisc_cb;
+	u32 drop_reason;
+
+	u16 zone; /* Only valid if post_ct = true */
+	u16 mru;
+	u8 post_ct:1;
+	u8 post_ct_snat:1;
+	u8 post_ct_dnat:1;
+};
+
+static inline struct tc_skb_cb *tc_skb_cb(const struct sk_buff *skb)
+{
+	struct tc_skb_cb *cb = (struct tc_skb_cb *)skb->cb;
+
+	BUILD_BUG_ON(sizeof(*cb) > sizeof_field(struct sk_buff, cb));
+	return cb;
+}
+
+static inline enum skb_drop_reason
+tcf_get_drop_reason(const struct sk_buff *skb)
+{
+	return tc_skb_cb(skb)->drop_reason;
+}
+
+static inline void tcf_set_drop_reason(const struct sk_buff *skb,
+				       enum skb_drop_reason reason)
+{
+	tc_skb_cb(skb)->drop_reason = reason;
+}
+
 /* Instead of calling kfree_skb() while root qdisc lock is held,
  * queue the skb for future freeing at end of __dev_xmit_skb()
  */

net/core/dev.c

@@ -3753,6 +3753,8 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
 
 	qdisc_calculate_pkt_len(skb, q);
 
+	tcf_set_drop_reason(skb, SKB_DROP_REASON_QDISC_DROP);
+
 	if (q->flags & TCQ_F_NOLOCK) {
 		if (q->flags & TCQ_F_CAN_BYPASS && nolock_qdisc_is_empty(q) &&
 		    qdisc_run_begin(q)) {
@@ -3782,7 +3784,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
 no_lock_out:
 		if (unlikely(to_free))
 			kfree_skb_list_reason(to_free,
-					      SKB_DROP_REASON_QDISC_DROP);
+					      tcf_get_drop_reason(to_free));
 		return rc;
 	}
 
@@ -3837,7 +3839,8 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
 	}
 	spin_unlock(root_lock);
 	if (unlikely(to_free))
-		kfree_skb_list_reason(to_free, SKB_DROP_REASON_QDISC_DROP);
+		kfree_skb_list_reason(to_free,
+				      tcf_get_drop_reason(to_free));
 	if (unlikely(contended))
 		spin_unlock(&q->busylock);
 	return rc;