Merge branch 'skb-drop-reasons'

Menglong Dong says:

====================
net: dev: add skb drop reasons to net/core/dev.c

In the commit c504e5c ("net: skb: introduce kfree_skb_reason()"),
we added the support of reporting the reasons of skb drops to kfree_skb
tracepoint. And in this series patches, reasons for skb drops are added
to the link layer, which means that 'net/core/dev.c' is our target.

Following functions are processed:

sch_handle_egress()
__dev_xmit_skb()
enqueue_to_backlog()
do_xdp_generic()
sch_handle_ingress()
__netif_receive_skb_core()

and following new drop reasons are added (what they mean can be see in
the document of them):

SKB_DROP_REASON_QDISC_EGRESS
SKB_DROP_REASON_QDISC_DROP
SKB_DROP_REASON_CPU_BACKLOG
SKB_DROP_REASON_XDP
SKB_DROP_REASON_QDISC_INGRESS
SKB_DROP_REASON_PTYPE_ABSENT

In order to add skb drop reasons to kfree_skb_list(), the function
kfree_skb_list_reason() is introduced in the 2th patch, which will be
used in __dev_xmit_skb() in the 3th patch.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -394,6 +394,24 @@ enum skb_drop_reason {
 						 * entry is full
 						 */
 	SKB_DROP_REASON_NEIGH_DEAD,	/* neigh entry is dead */
+	SKB_DROP_REASON_TC_EGRESS,	/* dropped in TC egress HOOK */
+	SKB_DROP_REASON_QDISC_DROP,	/* dropped by qdisc when packet
+					 * outputting (failed to enqueue to
+					 * current qdisc)
+					 */
+	SKB_DROP_REASON_CPU_BACKLOG,	/* failed to enqueue the skb to
+					 * the per CPU backlog queue. This
+					 * can be caused by backlog queue
+					 * full (see netdev_max_backlog in
+					 * net.rst) or RPS flow limit
+					 */
+	SKB_DROP_REASON_XDP,		/* dropped by XDP in input path */
+	SKB_DROP_REASON_TC_INGRESS,	/* dropped in TC ingress HOOK */
+	SKB_DROP_REASON_PTYPE_ABSENT,	/* not packet_type found to handle
+					 * the skb. For an etner packet,
+					 * this means that L3 protocol is
+					 * not supported
+					 */
 	SKB_DROP_REASON_MAX,
 };
 
@@ -1201,10 +1219,16 @@ static inline void kfree_skb(struct sk_buff *skb)
 }
 
 void skb_release_head_state(struct sk_buff *skb);
-void kfree_skb_list(struct sk_buff *segs);
+void kfree_skb_list_reason(struct sk_buff *segs,
+			   enum skb_drop_reason reason);
 void skb_dump(const char *level, const struct sk_buff *skb, bool full_pkt);
 void skb_tx_error(struct sk_buff *skb);
 
+static inline void kfree_skb_list(struct sk_buff *segs)
+{
+	kfree_skb_list_reason(segs, SKB_DROP_REASON_NOT_SPECIFIED);
+}
+
 #ifdef CONFIG_TRACEPOINTS
 void consume_skb(struct sk_buff *skb);
 #else

include/trace/events/skb.h

@@ -45,6 +45,12 @@
 	EM(SKB_DROP_REASON_NEIGH_FAILED, NEIGH_FAILED)		\
 	EM(SKB_DROP_REASON_NEIGH_QUEUEFULL, NEIGH_QUEUEFULL)	\
 	EM(SKB_DROP_REASON_NEIGH_DEAD, NEIGH_DEAD)		\
+	EM(SKB_DROP_REASON_TC_EGRESS, TC_EGRESS)		\
+	EM(SKB_DROP_REASON_QDISC_DROP, QDISC_DROP)		\
+	EM(SKB_DROP_REASON_CPU_BACKLOG, CPU_BACKLOG)		\
+	EM(SKB_DROP_REASON_XDP, XDP)				\
+	EM(SKB_DROP_REASON_TC_INGRESS, TC_INGRESS)		\
+	EM(SKB_DROP_REASON_PTYPE_ABSENT, PTYPE_ABSENT)		\
 	EMe(SKB_DROP_REASON_MAX, MAX)
 
 #undef EM

net/core/dev.c

@@ -3759,7 +3759,8 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
 
 no_lock_out:
 		if (unlikely(to_free))
-			kfree_skb_list(to_free);
+			kfree_skb_list_reason(to_free,
+					      SKB_DROP_REASON_QDISC_DROP);
 		return rc;
 	}
 
@@ -3814,7 +3815,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
 	}
 	spin_unlock(root_lock);
 	if (unlikely(to_free))
-		kfree_skb_list(to_free);
+		kfree_skb_list_reason(to_free, SKB_DROP_REASON_QDISC_DROP);
 	if (unlikely(contended))
 		spin_unlock(&q->busylock);
 	return rc;
@@ -3889,7 +3890,7 @@ sch_handle_egress(struct sk_buff *skb, int *ret, struct net_device *dev)
 	case TC_ACT_SHOT:
 		mini_qdisc_qstats_cpu_drop(miniq);
 		*ret = NET_XMIT_DROP;
-		kfree_skb(skb);
+		kfree_skb_reason(skb, SKB_DROP_REASON_TC_EGRESS);
 		return NULL;
 	case TC_ACT_STOLEN:
 	case TC_ACT_QUEUED:
@@ -4569,10 +4570,12 @@ static bool skb_flow_limit(struct sk_buff *skb, unsigned int qlen)
 static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
 			      unsigned int *qtail)
 {
+	enum skb_drop_reason reason;
 	struct softnet_data *sd;
 	unsigned long flags;
 	unsigned int qlen;
 
+	reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	sd = &per_cpu(softnet_data, cpu);
 
 	rps_lock_irqsave(sd, &flags);
@@ -4595,13 +4598,14 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
 			napi_schedule_rps(sd);
 		goto enqueue;
 	}
+	reason = SKB_DROP_REASON_CPU_BACKLOG;
 
 drop:
 	sd->dropped++;
 	rps_unlock_irq_restore(sd, &flags);
 
 	atomic_long_inc(&skb->dev->rx_dropped);
-	kfree_skb(skb);
+	kfree_skb_reason(skb, reason);
 	return NET_RX_DROP;
 }
 
@@ -4821,7 +4825,7 @@ int do_xdp_generic(struct bpf_prog *xdp_prog, struct sk_buff *skb)
 	}
 	return XDP_PASS;
 out_redir:
-	kfree_skb(skb);
+	kfree_skb_reason(skb, SKB_DROP_REASON_XDP);
 	return XDP_DROP;
 }
 EXPORT_SYMBOL_GPL(do_xdp_generic);
@@ -5037,7 +5041,7 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret,
 		break;
 	case TC_ACT_SHOT:
 		mini_qdisc_qstats_cpu_drop(miniq);
-		kfree_skb(skb);
+		kfree_skb_reason(skb, SKB_DROP_REASON_TC_INGRESS);
 		return NULL;
 	case TC_ACT_STOLEN:
 	case TC_ACT_QUEUED:
@@ -5354,11 +5358,13 @@ static int __netif_receive_skb_core(struct sk_buff **pskb, bool pfmemalloc,
 		*ppt_prev = pt_prev;
 	} else {
 drop:
-		if (!deliver_exact)
+		if (!deliver_exact) {
 			atomic_long_inc(&skb->dev->rx_dropped);
-		else
+			kfree_skb_reason(skb, SKB_DROP_REASON_PTYPE_ABSENT);
+		} else {
 			atomic_long_inc(&skb->dev->rx_nohandler);
-		kfree_skb(skb);
+			kfree_skb(skb);
+		}
 		/* Jamal, now you will not able to escape explaining
 		 * me how you were going to use this. :-)
 		 */

net/core/skbuff.c

@@ -777,16 +777,17 @@ void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
 }
 EXPORT_SYMBOL(kfree_skb_reason);
 
-void kfree_skb_list(struct sk_buff *segs)
+void kfree_skb_list_reason(struct sk_buff *segs,
+			   enum skb_drop_reason reason)
 {
 	while (segs) {
 		struct sk_buff *next = segs->next;
 
-		kfree_skb(segs);
+		kfree_skb_reason(segs, reason);
 		segs = next;
 	}
 }
-EXPORT_SYMBOL(kfree_skb_list);
+EXPORT_SYMBOL(kfree_skb_list_reason);
 
 /* Dump skb information and contents.
  *