net: netfilter: use kfree_drop_reason() for NF_DROP

Replace kfree_skb() with kfree_skb_reason() in nf_hook_slow() when
skb is dropped by reason of NF_DROP. Following new drop reasons
are introduced:

SKB_DROP_REASON_NETFILTER_DROP
Signed-off-by: Menglong Dong <imagedong@tencent.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -320,6 +320,7 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_TCP_CSUM,	/* TCP checksum error */
 	SKB_DROP_REASON_SOCKET_FILTER,	/* dropped by socket filter */
 	SKB_DROP_REASON_UDP_CSUM,	/* UDP checksum error */
+	SKB_DROP_REASON_NETFILTER_DROP,	/* dropped by netfilter */
 	SKB_DROP_REASON_MAX,
 };
 

include/trace/events/skb.h

@@ -16,6 +16,7 @@
 	EM(SKB_DROP_REASON_TCP_CSUM, TCP_CSUM)			\
 	EM(SKB_DROP_REASON_SOCKET_FILTER, SOCKET_FILTER)	\
 	EM(SKB_DROP_REASON_UDP_CSUM, UDP_CSUM)			\
+	EM(SKB_DROP_REASON_NETFILTER_DROP, NETFILTER_DROP)	\
 	EMe(SKB_DROP_REASON_MAX, MAX)
 
 #undef EM

net/netfilter/core.c

@@ -621,7 +621,8 @@ int nf_hook_slow(struct sk_buff *skb, struct nf_hook_state *state,
 		case NF_ACCEPT:
 			break;
 		case NF_DROP:
-			kfree_skb(skb);
+			kfree_skb_reason(skb,
+					 SKB_DROP_REASON_NETFILTER_DROP);
 			ret = NF_DROP_GETERR(verdict);
 			if (ret == 0)
 				ret = -EPERM;