[PATCH net-next v4 0/3] net: sched: Make tc-related drop reason more flexible for remaining qdiscs

[PATCH net-next v4 0/3] net: sched: Make tc-related drop reason more flexible for remaining qdiscs

[Victor Nogueira]

This patch builds on Daniel's patch[1] to add initial support of tc drop
reason. The main goal is to distinguish between policy and error drops for
the remainder of the egress qdiscs (other than clsact).
The drop reason is set by cls_api and act_api in the tc skb cb in case
any error occurred in the data path.

Also add new skb drop reasons that are idiosyncratic to TC.

[1] https://lore.kernel.org/all/20231009092655.22025-1-daniel@iogearbox.net

Changes in V4:
- Condense all the cookie drop reasons into one

Changes in V3:
- Removed duplicate assignment
- Rename function tc_skb_cb_drop_reason to tcf_get_drop_reason
- Move zone field upwards in struct tc_skb_cb to move hole to the end of 
  the struct

Changes in V2:
- Dropped RFC tag
- Removed check for drop reason being overwritten by filter in cls_api.c
- Simplified logic and removed function tcf_init_drop_reason

Victor Nogueira (3):
  net: sched: Move drop_reason to struct tc_skb_cb
  net: sched: Make tc-related drop reason more flexible for remaining
    qdiscs
  net: sched: Add initial TC error skb drop reasons

 include/net/dropreason-core.h | 18 +++++++++++++++---
 include/net/pkt_cls.h         |  6 ------
 include/net/pkt_sched.h       | 18 ------------------
 include/net/sch_generic.h     | 32 +++++++++++++++++++++++++++++++-
 net/core/dev.c                | 11 +++++++----
 net/sched/act_api.c           |  3 ++-
 net/sched/cls_api.c           | 31 +++++++++++++++----------------
 7 files changed, 70 insertions(+), 49 deletions(-)

-- 
2.25.1

[PATCH net-next v4 1/3] net: sched: Move drop_reason to struct tc_skb_cb

[Victor Nogueira]

Move drop_reason from struct tcf_result to skb cb - more specifically to
struct tc_skb_cb. With that, we'll be able to also set the drop reason for
the remaining qdiscs (aside from clsact) that do not have access to
tcf_result when time comes to set the skb drop reason.

Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Simon Horman <horms@kernel.org>
---
 include/net/pkt_cls.h     | 14 ++++++++++++--
 include/net/pkt_sched.h   |  3 ++-
 include/net/sch_generic.h |  1 -
 net/core/dev.c            |  4 ++--
 net/sched/act_api.c       |  2 +-
 net/sched/cls_api.c       | 23 ++++++++---------------
 6 files changed, 25 insertions(+), 22 deletions(-)

diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index a76c9171db0e..761e4500cca0 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -154,10 +154,20 @@ __cls_set_class(unsigned long *clp, unsigned long cl)
 	return xchg(clp, cl);
 }
 
-static inline void tcf_set_drop_reason(struct tcf_result *res,
+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)
 {
-	res->drop_reason = reason;
+	tc_skb_cb(skb)->drop_reason = reason;
 }
 
 static inline void
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 9fa1d0794dfa..9b559aa5c079 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -277,12 +277,13 @@ static inline void skb_txtime_consumed(struct sk_buff *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;
-	u16 zone; /* Only valid if post_ct = true */
 };
 
 static inline struct tc_skb_cb *tc_skb_cb(const struct sk_buff *skb)
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index dcb9160e6467..c499b56bb215 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -332,7 +332,6 @@ struct tcf_result {
 		};
 		const struct tcf_proto *goto_tp;
 	};
-	enum skb_drop_reason		drop_reason;
 };
 
 struct tcf_chain;
diff --git a/net/core/dev.c b/net/core/dev.c
index 0432b04cf9b0..16af89a733e4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3923,14 +3923,14 @@ static int tc_run(struct tcx_entry *entry, struct sk_buff *skb,
 
 	tc_skb_cb(skb)->mru = 0;
 	tc_skb_cb(skb)->post_ct = false;
-	res.drop_reason = *drop_reason;
+	tcf_set_drop_reason(skb, *drop_reason);
 
 	mini_qdisc_bstats_cpu_update(miniq, skb);
 	ret = tcf_classify(skb, miniq->block, miniq->filter_list, &res, false);
 	/* Only tcf related quirks below. */
 	switch (ret) {
 	case TC_ACT_SHOT:
-		*drop_reason = res.drop_reason;
+		*drop_reason = tcf_get_drop_reason(skb);
 		mini_qdisc_qstats_cpu_drop(miniq);
 		break;
 	case TC_ACT_OK:
diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index 3a7770eff52d..db500aa9f841 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -1119,7 +1119,7 @@ int tcf_action_exec(struct sk_buff *skb, struct tc_action **actions,
 			}
 		} else if (TC_ACT_EXT_CMP(ret, TC_ACT_GOTO_CHAIN)) {
 			if (unlikely(!rcu_access_pointer(a->goto_chain))) {
-				tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
+				tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
 				return TC_ACT_SHOT;
 			}
 			tcf_action_goto_chain_exec(a, res);
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index dc1c19a25882..199406e4bcdd 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -1657,7 +1657,6 @@ static inline int __tcf_classify(struct sk_buff *skb,
 				 int act_index,
 				 u32 *last_executed_chain)
 {
-	u32 orig_reason = res->drop_reason;
 #ifdef CONFIG_NET_CLS_ACT
 	const int max_reclassify_loop = 16;
 	const struct tcf_proto *first_tp;
@@ -1682,13 +1681,13 @@ static inline int __tcf_classify(struct sk_buff *skb,
 			 */
 			if (unlikely(n->tp != tp || n->tp->chain != n->chain ||
 				     !tp->ops->get_exts)) {
-				tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
+				tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
 				return TC_ACT_SHOT;
 			}
 
 			exts = tp->ops->get_exts(tp, n->handle);
 			if (unlikely(!exts || n->exts != exts)) {
-				tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
+				tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
 				return TC_ACT_SHOT;
 			}
 
@@ -1712,18 +1711,12 @@ static inline int __tcf_classify(struct sk_buff *skb,
 			goto reset;
 		}
 #endif
-		if (err >= 0) {
-			/* Policy drop or drop reason is over-written by
-			 * classifiers with a bogus value(0) */
-			if (err == TC_ACT_SHOT &&
-			    res->drop_reason == SKB_NOT_DROPPED_YET)
-				tcf_set_drop_reason(res, orig_reason);
+		if (err >= 0)
 			return err;
-		}
 	}
 
 	if (unlikely(n)) {
-		tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
+		tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
 		return TC_ACT_SHOT;
 	}
 
@@ -1735,7 +1728,7 @@ static inline int __tcf_classify(struct sk_buff *skb,
 				       tp->chain->block->index,
 				       tp->prio & 0xffff,
 				       ntohs(tp->protocol));
-		tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
+		tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
 		return TC_ACT_SHOT;
 	}
 
@@ -1773,7 +1766,7 @@ int tcf_classify(struct sk_buff *skb,
 				n = tcf_exts_miss_cookie_lookup(ext->act_miss_cookie,
 								&act_index);
 				if (!n) {
-					tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
+					tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
 					return TC_ACT_SHOT;
 				}
 
@@ -1784,7 +1777,7 @@ int tcf_classify(struct sk_buff *skb,
 
 			fchain = tcf_chain_lookup_rcu(block, chain);
 			if (!fchain) {
-				tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
+				tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
 				return TC_ACT_SHOT;
 			}
 
@@ -1806,7 +1799,7 @@ int tcf_classify(struct sk_buff *skb,
 
 			ext = tc_skb_ext_alloc(skb);
 			if (WARN_ON_ONCE(!ext)) {
-				tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
+				tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
 				return TC_ACT_SHOT;
 			}
 
-- 
2.25.1

[PATCH net-next v4 2/3] net: sched: Make tc-related drop reason more flexible for remaining qdiscs

[Victor Nogueira]

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.net

Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Simon Horman <horms@kernel.org>
---
 include/net/pkt_cls.h     | 16 ----------------
 include/net/pkt_sched.h   | 19 -------------------
 include/net/sch_generic.h | 31 +++++++++++++++++++++++++++++++
 net/core/dev.c            |  7 +++++--
 4 files changed, 36 insertions(+), 37 deletions(-)

diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index 761e4500cca0..f308e8268651 100644
--- a/include/net/pkt_cls.h
+++ b/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)
 {
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 9b559aa5c079..1e200d9a066d 100644
--- a/include/net/pkt_sched.h
+++ b/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)
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index c499b56bb215..1d70c2c1572f 100644
--- a/include/net/sch_generic.h
+++ b/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()
  */
diff --git a/net/core/dev.c b/net/core/dev.c
index 16af89a733e4..b87504078320 100644
--- a/net/core/dev.c
+++ b/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;
-- 
2.25.1

[PATCH net-next v4 3/3] net: sched: Add initial TC error skb drop reasons

[Victor Nogueira]

Continue expanding Daniel's patch by adding new skb drop reasons that
are idiosyncratic to TC.

More specifically:

- SKB_DROP_REASON_TC_EXT_COOKIE_ERROR: An error occurred whilst
  processing a tc ext cookie.

- SKB_DROP_REASON_TC_CHAIN_NOTFOUND: tc chain lookup failed.

- SKB_DROP_REASON_TC_RECLASSIFY_LOOP: tc exceeded max reclassify loop
  iterations

Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Reviewed-by: Simon Horman <horms@kernel.org>
---
 include/net/dropreason-core.h | 18 +++++++++++++++---
 net/sched/act_api.c           |  3 ++-
 net/sched/cls_api.c           | 22 ++++++++++++++--------
 3 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index 278e4c7d465c..dea361b3555d 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -85,8 +85,10 @@
 	FN(IPV6_NDISC_BAD_OPTIONS)	\
 	FN(IPV6_NDISC_NS_OTHERHOST)	\
 	FN(QUEUE_PURGE)			\
-	FN(TC_ERROR)			\
+	FN(TC_COOKIE_ERROR)		\
 	FN(PACKET_SOCK_ERROR)		\
+	FN(TC_CHAIN_NOTFOUND)		\
+	FN(TC_RECLASSIFY_LOOP)		\
 	FNe(MAX)
 
 /**
@@ -377,13 +379,23 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST,
 	/** @SKB_DROP_REASON_QUEUE_PURGE: bulk free. */
 	SKB_DROP_REASON_QUEUE_PURGE,
-	/** @SKB_DROP_REASON_TC_ERROR: generic internal tc error. */
-	SKB_DROP_REASON_TC_ERROR,
+	/**
+	 * @SKB_DROP_REASON_TC_EXT_COOKIE_ERROR: An error occurred whilst
+	 * processing a tc ext cookie.
+	 */
+	SKB_DROP_REASON_TC_COOKIE_ERROR,
 	/**
 	 * @SKB_DROP_REASON_PACKET_SOCK_ERROR: generic packet socket errors
 	 * after its filter matches an incoming packet.
 	 */
 	SKB_DROP_REASON_PACKET_SOCK_ERROR,
+	/** @SKB_DROP_REASON_TC_CHAIN_NOTFOUND: tc chain lookup failed. */
+	SKB_DROP_REASON_TC_CHAIN_NOTFOUND,
+	/**
+	 * @SKB_DROP_REASON_TC_RECLASSIFY_LOOP: tc exceeded max reclassify loop
+	 * iterations.
+	 */
+	SKB_DROP_REASON_TC_RECLASSIFY_LOOP,
 	/**
 	 * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
 	 * shouldn't be used as a real 'reason' - only for tracing code gen
diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index db500aa9f841..a44c097a880d 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -1119,7 +1119,8 @@ int tcf_action_exec(struct sk_buff *skb, struct tc_action **actions,
 			}
 		} else if (TC_ACT_EXT_CMP(ret, TC_ACT_GOTO_CHAIN)) {
 			if (unlikely(!rcu_access_pointer(a->goto_chain))) {
-				tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
+				tcf_set_drop_reason(skb,
+						    SKB_DROP_REASON_TC_CHAIN_NOTFOUND);
 				return TC_ACT_SHOT;
 			}
 			tcf_action_goto_chain_exec(a, res);
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 199406e4bcdd..8978cf5531d0 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -1681,13 +1681,15 @@ static inline int __tcf_classify(struct sk_buff *skb,
 			 */
 			if (unlikely(n->tp != tp || n->tp->chain != n->chain ||
 				     !tp->ops->get_exts)) {
-				tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
+				tcf_set_drop_reason(skb,
+						    SKB_DROP_REASON_TC_COOKIE_ERROR);
 				return TC_ACT_SHOT;
 			}
 
 			exts = tp->ops->get_exts(tp, n->handle);
 			if (unlikely(!exts || n->exts != exts)) {
-				tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
+				tcf_set_drop_reason(skb,
+						    SKB_DROP_REASON_TC_COOKIE_ERROR);
 				return TC_ACT_SHOT;
 			}
 
@@ -1716,7 +1718,8 @@ static inline int __tcf_classify(struct sk_buff *skb,
 	}
 
 	if (unlikely(n)) {
-		tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
+		tcf_set_drop_reason(skb,
+				    SKB_DROP_REASON_TC_COOKIE_ERROR);
 		return TC_ACT_SHOT;
 	}
 
@@ -1728,7 +1731,8 @@ static inline int __tcf_classify(struct sk_buff *skb,
 				       tp->chain->block->index,
 				       tp->prio & 0xffff,
 				       ntohs(tp->protocol));
-		tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
+		tcf_set_drop_reason(skb,
+				    SKB_DROP_REASON_TC_RECLASSIFY_LOOP);
 		return TC_ACT_SHOT;
 	}
 
@@ -1766,7 +1770,8 @@ int tcf_classify(struct sk_buff *skb,
 				n = tcf_exts_miss_cookie_lookup(ext->act_miss_cookie,
 								&act_index);
 				if (!n) {
-					tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
+					tcf_set_drop_reason(skb,
+							    SKB_DROP_REASON_TC_COOKIE_ERROR);
 					return TC_ACT_SHOT;
 				}
 
@@ -1777,7 +1782,9 @@ int tcf_classify(struct sk_buff *skb,
 
 			fchain = tcf_chain_lookup_rcu(block, chain);
 			if (!fchain) {
-				tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
+				tcf_set_drop_reason(skb,
+						    SKB_DROP_REASON_TC_CHAIN_NOTFOUND);
+
 				return TC_ACT_SHOT;
 			}
 
@@ -1799,10 +1806,9 @@ int tcf_classify(struct sk_buff *skb,
 
 			ext = tc_skb_ext_alloc(skb);
 			if (WARN_ON_ONCE(!ext)) {
-				tcf_set_drop_reason(skb, SKB_DROP_REASON_TC_ERROR);
+				tcf_set_drop_reason(skb, SKB_DROP_REASON_NOMEM);
 				return TC_ACT_SHOT;
 			}
-
 			ext->chain = last_executed_chain;
 			ext->mru = cb->mru;
 			ext->post_ct = cb->post_ct;
-- 
2.25.1

Re: [PATCH net-next v4 3/3] net: sched: Add initial TC error skb drop reasons

[Simon Horman]

On Thu, Dec 14, 2023 at 05:35:32PM -0300, Victor Nogueira wrote:
> Continue expanding Daniel's patch by adding new skb drop reasons that
> are idiosyncratic to TC.
> 
> More specifically:
> 
> - SKB_DROP_REASON_TC_EXT_COOKIE_ERROR: An error occurred whilst
>   processing a tc ext cookie.
> 
> - SKB_DROP_REASON_TC_CHAIN_NOTFOUND: tc chain lookup failed.
> 
> - SKB_DROP_REASON_TC_RECLASSIFY_LOOP: tc exceeded max reclassify loop
>   iterations
> 
> Signed-off-by: Victor Nogueira <victor@mojatatu.com>
> Reviewed-by: Simon Horman <horms@kernel.org>
> ---
>  include/net/dropreason-core.h | 18 +++++++++++++++---
>  net/sched/act_api.c           |  3 ++-
>  net/sched/cls_api.c           | 22 ++++++++++++++--------
>  3 files changed, 31 insertions(+), 12 deletions(-)
> 
> diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
> index 278e4c7d465c..dea361b3555d 100644
> --- a/include/net/dropreason-core.h
> +++ b/include/net/dropreason-core.h
> @@ -85,8 +85,10 @@
>  	FN(IPV6_NDISC_BAD_OPTIONS)	\
>  	FN(IPV6_NDISC_NS_OTHERHOST)	\
>  	FN(QUEUE_PURGE)			\
> -	FN(TC_ERROR)			\
> +	FN(TC_COOKIE_ERROR)		\
>  	FN(PACKET_SOCK_ERROR)		\
> +	FN(TC_CHAIN_NOTFOUND)		\
> +	FN(TC_RECLASSIFY_LOOP)		\
>  	FNe(MAX)
>  
>  /**
> @@ -377,13 +379,23 @@ enum skb_drop_reason {
>  	SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST,
>  	/** @SKB_DROP_REASON_QUEUE_PURGE: bulk free. */
>  	SKB_DROP_REASON_QUEUE_PURGE,
> -	/** @SKB_DROP_REASON_TC_ERROR: generic internal tc error. */
> -	SKB_DROP_REASON_TC_ERROR,
> +	/**
> +	 * @SKB_DROP_REASON_TC_EXT_COOKIE_ERROR: An error occurred whilst

nit: @SKB_DROP_REASON_TC_COOKIE_ERROR

> +	 * processing a tc ext cookie.
> +	 */
> +	SKB_DROP_REASON_TC_COOKIE_ERROR,
>  	/**
>  	 * @SKB_DROP_REASON_PACKET_SOCK_ERROR: generic packet socket errors
>  	 * after its filter matches an incoming packet.
>  	 */
>  	SKB_DROP_REASON_PACKET_SOCK_ERROR,
> +	/** @SKB_DROP_REASON_TC_CHAIN_NOTFOUND: tc chain lookup failed. */
> +	SKB_DROP_REASON_TC_CHAIN_NOTFOUND,
> +	/**
> +	 * @SKB_DROP_REASON_TC_RECLASSIFY_LOOP: tc exceeded max reclassify loop
> +	 * iterations.
> +	 */
> +	SKB_DROP_REASON_TC_RECLASSIFY_LOOP,
>  	/**
>  	 * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
>  	 * shouldn't be used as a real 'reason' - only for tracing code gen

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