[PATCH net-next 2/2] net: skb: use kfree_skb_with_reason() in tcp_v4_rcv()

[menglong8.dong@gmail.com]

From: Menglong Dong <imagedong@tencent.com>

Replace kfree_skb() with kfree_skb_with_reason() in tcp_v4_rcv().
Following drop reason are added:

SKB_DROP_REASON_NO_SOCK
SKB_DROP_REASON_BAD_PACKET
SKB_DROP_REASON_TCP_CSUM

After this patch, 'kfree_skb' event will print message like this:

$           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
$              | |         |   |||||     |         |
          <idle>-0       [000] ..s1.    36.113438: kfree_skb: skbaddr=(____ptrval____) protocol=2048 location=(____ptrval____) reason: NO_SOCK

The reason of skb drop is printed too.

Signed-off-by: Menglong Dong <imagedong@tencent.com>
---
 include/linux/skbuff.h     |  3 +++
 include/trace/events/skb.h |  3 +++
 net/ipv4/tcp_ipv4.c        | 10 ++++++++--
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 3620b3ff2154..f85db6c035d1 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -313,6 +313,9 @@ struct sk_buff;
  */
 enum skb_drop_reason {
 	SKB_DROP_REASON_NOT_SPECIFIED,
+	SKB_DROP_REASON_NO_SOCK,
+	SKB_DROP_REASON_BAD_PACKET,
+	SKB_DROP_REASON_TCP_CSUM,
 	SKB_DROP_REASON_MAX,
 };
 
diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index cab1c08a30cd..b9ea6b4ed7ec 100644
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -11,6 +11,9 @@
 
 #define TRACE_SKB_DROP_REASON					\
 	EM(SKB_DROP_REASON_NOT_SPECIFIED, NOT_SPECIFIED)	\
+	EM(SKB_DROP_REASON_NO_SOCK, NO_SOCK)			\
+	EM(SKB_DROP_REASON_BAD_PACKET, BAD_PACKET)		\
+	EM(SKB_DROP_REASON_TCP_CSUM, TCP_CSUM)			\
 	EMe(SKB_DROP_REASON_MAX, HAHA_MAX)
 
 #undef EM
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index ac10e4cdd8d0..03dc4c79b84b 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1971,8 +1971,10 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	const struct tcphdr *th;
 	bool refcounted;
 	struct sock *sk;
+	int drop_reason;
 	int ret;
 
+	drop_reason = 0;
 	if (skb->pkt_type != PACKET_HOST)
 		goto discard_it;
 
@@ -1984,8 +1986,10 @@ int tcp_v4_rcv(struct sk_buff *skb)
 
 	th = (const struct tcphdr *)skb->data;
 
-	if (unlikely(th->doff < sizeof(struct tcphdr) / 4))
+	if (unlikely(th->doff < sizeof(struct tcphdr) / 4)) {
+		drop_reason = SKB_DROP_REASON_BAD_PACKET;
 		goto bad_packet;
+	}
 	if (!pskb_may_pull(skb, th->doff * 4))
 		goto discard_it;
 
@@ -2124,6 +2128,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	return ret;
 
 no_tcp_socket:
+	drop_reason = SKB_DROP_REASON_NO_SOCK;
 	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
 		goto discard_it;
 
@@ -2131,6 +2136,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 
 	if (tcp_checksum_complete(skb)) {
 csum_error:
+		drop_reason = SKB_DROP_REASON_TCP_CSUM;
 		trace_tcp_bad_csum(skb);
 		__TCP_INC_STATS(net, TCP_MIB_CSUMERRORS);
 bad_packet:
@@ -2141,7 +2147,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 
 discard_it:
 	/* Discard frame. */
-	kfree_skb(skb);
+	kfree_skb_with_reason(skb, drop_reason);
 	return 0;
 
 discard_and_relse:
-- 
2.30.2