[PATCH RFC 1/4] net: skb: use line number to trace dropped skb

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Sometimes the kernel may not directly call kfree_skb() to drop the sk_buff.
Instead, it "goto drop" and call kfree_skb() at 'drop'. This make it
difficult to track the reason that the sk_buff is dropped.

The commit c504e5c2f964 ("net: skb: introduce kfree_skb_reason()") has
introduced the kfree_skb_reason() to help track the reason. However, we may
need to define many reasons for each driver/subsystem.

To avoid introducing so many new reasons, this is to use line number
("__LINE__") to trace where the sk_buff is dropped. As a result, the reason
will be generated automatically.

Cc: Joao Martins <joao.m.martins@xxxxxxxxxx>
Cc: Joe Jin <joe.jin@xxxxxxxxxx>
Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
---
 include/linux/skbuff.h     | 21 ++++-----------------
 include/trace/events/skb.h | 35 ++++++-----------------------------
 net/core/dev.c             |  2 +-
 net/core/skbuff.c          |  9 ++++-----
 net/ipv4/tcp_ipv4.c        | 14 +++++++-------
 net/ipv4/udp.c             | 14 +++++++-------
 6 files changed, 29 insertions(+), 66 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8a636e678902..471268a4a497 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -307,21 +307,8 @@ struct sk_buff_head {
 
 struct sk_buff;
 
-/* The reason of skb drop, which is used in kfree_skb_reason().
- * en...maybe they should be splited by group?
- *
- * Each item here should also be in 'TRACE_SKB_DROP_REASON', which is
- * used to translate the reason to string.
- */
-enum skb_drop_reason {
-	SKB_DROP_REASON_NOT_SPECIFIED,
-	SKB_DROP_REASON_NO_SOCKET,
-	SKB_DROP_REASON_PKT_TOO_SMALL,
-	SKB_DROP_REASON_TCP_CSUM,
-	SKB_DROP_REASON_SOCKET_FILTER,
-	SKB_DROP_REASON_UDP_CSUM,
-	SKB_DROP_REASON_MAX,
-};
+#define SKB_DROP_LINE_NONE	0
+#define SKB_DROP_LINE		__LINE__
 
 /* To allow 64K frame to be packed as single skb without frag_list we
  * require 64K/PAGE_SIZE pages plus 1 additional page to allow for
@@ -1103,7 +1090,7 @@ static inline bool skb_unref(struct sk_buff *skb)
 	return true;
 }
 
-void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason);
+void kfree_skb_reason(struct sk_buff *skb, unsigned int line);
 
 /**
  *	kfree_skb - free an sk_buff with 'NOT_SPECIFIED' reason
@@ -1111,7 +1098,7 @@ void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason);
  */
 static inline void kfree_skb(struct sk_buff *skb)
 {
-	kfree_skb_reason(skb, SKB_DROP_REASON_NOT_SPECIFIED);
+	kfree_skb_reason(skb, SKB_DROP_LINE_NONE);
 }
 
 void skb_release_head_state(struct sk_buff *skb);
diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index a8a64b97504d..45d1a1757ff1 100644
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -9,56 +9,33 @@
 #include <linux/netdevice.h>
 #include <linux/tracepoint.h>
 
-#define TRACE_SKB_DROP_REASON					\
-	EM(SKB_DROP_REASON_NOT_SPECIFIED, NOT_SPECIFIED)	\
-	EM(SKB_DROP_REASON_NO_SOCKET, NO_SOCKET)		\
-	EM(SKB_DROP_REASON_PKT_TOO_SMALL, PKT_TOO_SMALL)	\
-	EM(SKB_DROP_REASON_TCP_CSUM, TCP_CSUM)			\
-	EM(SKB_DROP_REASON_SOCKET_FILTER, SOCKET_FILTER)	\
-	EM(SKB_DROP_REASON_UDP_CSUM, UDP_CSUM)			\
-	EMe(SKB_DROP_REASON_MAX, MAX)
-
-#undef EM
-#undef EMe
-
-#define EM(a, b)	TRACE_DEFINE_ENUM(a);
-#define EMe(a, b)	TRACE_DEFINE_ENUM(a);
-
-TRACE_SKB_DROP_REASON
-
-#undef EM
-#undef EMe
-#define EM(a, b)	{ a, #b },
-#define EMe(a, b)	{ a, #b }
-
 /*
  * Tracepoint for free an sk_buff:
  */
 TRACE_EVENT(kfree_skb,
 
 	TP_PROTO(struct sk_buff *skb, void *location,
-		 enum skb_drop_reason reason),
+		 unsigned int line),
 
-	TP_ARGS(skb, location, reason),
+	TP_ARGS(skb, location, line),
 
 	TP_STRUCT__entry(
 		__field(void *,		skbaddr)
 		__field(void *,		location)
 		__field(unsigned short,	protocol)
-		__field(enum skb_drop_reason,	reason)
+		__field(unsigned int,	line)
 	),
 
 	TP_fast_assign(
 		__entry->skbaddr = skb;
 		__entry->location = location;
 		__entry->protocol = ntohs(skb->protocol);
-		__entry->reason = reason;
+		__entry->line = line;
 	),
 
-	TP_printk("skbaddr=%p protocol=%u location=%p reason: %s",
+	TP_printk("skbaddr=%p protocol=%u location=%p line: %u",
 		  __entry->skbaddr, __entry->protocol, __entry->location,
-		  __print_symbolic(__entry->reason,
-				   TRACE_SKB_DROP_REASON))
+		  __entry->line)
 );
 
 TRACE_EVENT(consume_skb,
diff --git a/net/core/dev.c b/net/core/dev.c
index 1baab07820f6..448f390d35d3 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4900,7 +4900,7 @@ static __latent_entropy void net_tx_action(struct softirq_action *h)
 				trace_consume_skb(skb);
 			else
 				trace_kfree_skb(skb, net_tx_action,
-						SKB_DROP_REASON_NOT_SPECIFIED);
+						SKB_DROP_LINE);
 
 			if (skb->fclone != SKB_FCLONE_UNAVAILABLE)
 				__kfree_skb(skb);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 0118f0afaa4f..8572c3bce264 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -761,18 +761,17 @@ EXPORT_SYMBOL(__kfree_skb);
 /**
  *	kfree_skb_reason - free an sk_buff with special reason
  *	@skb: buffer to free
- *	@reason: reason why this skb is dropped
+ *	@line: the line where this skb is dropped
  *
  *	Drop a reference to the buffer and free it if the usage count has
- *	hit zero. Meanwhile, pass the drop reason to 'kfree_skb'
- *	tracepoint.
+ *	hit zero. Meanwhile, pass the drop line to 'kfree_skb' tracepoint.
  */
-void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
+void kfree_skb_reason(struct sk_buff *skb, unsigned int line)
 {
 	if (!skb_unref(skb))
 		return;
 
-	trace_kfree_skb(skb, __builtin_return_address(0), reason);
+	trace_kfree_skb(skb, __builtin_return_address(0), line);
 	__kfree_skb(skb);
 }
 EXPORT_SYMBOL(kfree_skb_reason);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index fec656f5a39e..f23af94d1186 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1971,10 +1971,10 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	const struct tcphdr *th;
 	bool refcounted;
 	struct sock *sk;
-	int drop_reason;
+	unsigned int drop_line;
 	int ret;
 
-	drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;
+	drop_line = SKB_DROP_LINE_NONE;
 	if (skb->pkt_type != PACKET_HOST)
 		goto discard_it;
 
@@ -1987,7 +1987,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	th = (const struct tcphdr *)skb->data;
 
 	if (unlikely(th->doff < sizeof(struct tcphdr) / 4)) {
-		drop_reason = SKB_DROP_REASON_PKT_TOO_SMALL;
+		drop_line = SKB_DROP_LINE;
 		goto bad_packet;
 	}
 	if (!pskb_may_pull(skb, th->doff * 4))
@@ -2095,7 +2095,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	nf_reset_ct(skb);
 
 	if (tcp_filter(sk, skb)) {
-		drop_reason = SKB_DROP_REASON_SOCKET_FILTER;
+		drop_line = SKB_DROP_LINE;
 		goto discard_and_relse;
 	}
 	th = (const struct tcphdr *)skb->data;
@@ -2130,7 +2130,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	return ret;
 
 no_tcp_socket:
-	drop_reason = SKB_DROP_REASON_NO_SOCKET;
+	drop_line = SKB_DROP_LINE;
 	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
 		goto discard_it;
 
@@ -2138,7 +2138,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 
 	if (tcp_checksum_complete(skb)) {
 csum_error:
-		drop_reason = SKB_DROP_REASON_TCP_CSUM;
+		drop_line = SKB_DROP_LINE;
 		trace_tcp_bad_csum(skb);
 		__TCP_INC_STATS(net, TCP_MIB_CSUMERRORS);
 bad_packet:
@@ -2149,7 +2149,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 
 discard_it:
 	/* Discard frame. */
-	kfree_skb_reason(skb, drop_reason);
+	kfree_skb_reason(skb, drop_line);
 	return 0;
 
 discard_and_relse:
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 090360939401..f0715d1072d7 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2411,9 +2411,9 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	__be32 saddr, daddr;
 	struct net *net = dev_net(skb->dev);
 	bool refcounted;
-	int drop_reason;
+	unsigned int drop_line;
 
-	drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;
+	drop_line = SKB_DROP_LINE_NONE;
 
 	/*
 	 *  Validate the packet.
@@ -2469,7 +2469,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	if (udp_lib_checksum_complete(skb))
 		goto csum_error;
 
-	drop_reason = SKB_DROP_REASON_NO_SOCKET;
+	drop_line = SKB_DROP_LINE;
 	__UDP_INC_STATS(net, UDP_MIB_NOPORTS, proto == IPPROTO_UDPLITE);
 	icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
 
@@ -2477,11 +2477,11 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	 * Hmm.  We got an UDP packet to a port to which we
 	 * don't wanna listen.  Ignore it.
 	 */
-	kfree_skb_reason(skb, drop_reason);
+	kfree_skb_reason(skb, drop_line);
 	return 0;
 
 short_packet:
-	drop_reason = SKB_DROP_REASON_PKT_TOO_SMALL;
+	drop_line = SKB_DROP_LINE;
 	net_dbg_ratelimited("UDP%s: short packet: From %pI4:%u %d/%d to %pI4:%u\n",
 			    proto == IPPROTO_UDPLITE ? "Lite" : "",
 			    &saddr, ntohs(uh->source),
@@ -2494,7 +2494,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	 * RFC1122: OK.  Discards the bad packet silently (as far as
 	 * the network is concerned, anyway) as per 4.1.3.4 (MUST).
 	 */
-	drop_reason = SKB_DROP_REASON_UDP_CSUM;
+	drop_line = SKB_DROP_LINE;
 	net_dbg_ratelimited("UDP%s: bad checksum. From %pI4:%u to %pI4:%u ulen %d\n",
 			    proto == IPPROTO_UDPLITE ? "Lite" : "",
 			    &saddr, ntohs(uh->source), &daddr, ntohs(uh->dest),
@@ -2502,7 +2502,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	__UDP_INC_STATS(net, UDP_MIB_CSUMERRORS, proto == IPPROTO_UDPLITE);
 drop:
 	__UDP_INC_STATS(net, UDP_MIB_INERRORS, proto == IPPROTO_UDPLITE);
-	kfree_skb_reason(skb, drop_reason);
+	kfree_skb_reason(skb, drop_line);
 	return 0;
 }
 
-- 
2.17.1




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