Merge branch 'net-skb-introduce-kfree_skb_with_reason'

Menglong Dong says:

====================
net: skb: introduce kfree_skb_with_reason()

In this series patch, the interface kfree_skb_with_reason() is
introduced(), which is used to collect skb drop reason, and pass
it to 'kfree_skb' tracepoint. Therefor, 'drop_monitor' or eBPF is
able to monitor abnormal skb with detail reason.

In fact, this series patches are out of the intelligence of David
and Steve, I'm just a truck man :/

Previous discussion is here:

https://lore.kernel.org/netdev/20211118105752.1d46e990@gandalf.local.home/
https://lore.kernel.org/netdev/67b36bd8-2477-88ac-83a0-35a1eeaf40c9@gmail.com/

In the first patch, kfree_skb_with_reason() is introduced and
the 'reason' field is added to 'kfree_skb' tracepoint. In the
second patch, 'kfree_skb()' in replaced with 'kfree_skb_with_reason()'
in tcp_v4_rcv(). In the third patch, 'kfree_skb_with_reason()' is
used in __udp4_lib_rcv().

Changes since v3:
- fix some code style problems in skb.h

Changes since v2:
- rename kfree_skb_with_reason() to kfree_skb_reason()
- make kfree_skb() static inline, as Jakub suggested

Changes since v1:
- rename some drop reason, as David suggested
- add the third patch
====================

Link: https://lore.kernel.org/r/20220109063628.526990-1-imagedong@tencent.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 61 insertions, 8 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 642acb0d1646..af64c7de9b53 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -305,6 +305,22 @@ 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_TCP_FILTER,
+	SKB_DROP_REASON_UDP_CSUM,
+	SKB_DROP_REASON_MAX,
+};
+
 /* 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
  * buffers which do not start on a page boundary.
@@ -1085,8 +1101,18 @@ static inline bool skb_unref(struct sk_buff *skb)
 	return true;
 }
 
+void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason);
+
+/**
+ *	kfree_skb - free an sk_buff with 'NOT_SPECIFIED' reason
+ *	@skb: buffer to free
+ */
+static inline void kfree_skb(struct sk_buff *skb)
+{
+	kfree_skb_reason(skb, SKB_DROP_REASON_NOT_SPECIFIED);
+}
+
 void skb_release_head_state(struct sk_buff *skb);
-void kfree_skb(struct sk_buff *skb);
 void kfree_skb_list(struct sk_buff *segs);
 void skb_dump(const char *level, const struct sk_buff *skb, bool full_pkt);
 void skb_tx_error(struct sk_buff *skb);
diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index 9e92f22eb086..3e042ca2cedb 100644
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -9,29 +9,56 @@
 #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_TCP_FILTER, TCP_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),
+	TP_PROTO(struct sk_buff *skb, void *location,
+		 enum skb_drop_reason reason),
 
-	TP_ARGS(skb, location),
+	TP_ARGS(skb, location, reason),
 
 	TP_STRUCT__entry(
-		__field(	void *,		skbaddr		)
-		__field(	void *,		location	)
-		__field(	unsigned short,	protocol	)
+		__field(void *,		skbaddr)
+		__field(void *,		location)
+		__field(unsigned short,	protocol)
+		__field(enum skb_drop_reason,	reason)
 	),
 
 	TP_fast_assign(
 		__entry->skbaddr = skb;
 		__entry->location = location;
 		__entry->protocol = ntohs(skb->protocol);
+		__entry->reason = reason;
 	),
 
-	TP_printk("skbaddr=%p protocol=%u location=%p",
-		__entry->skbaddr, __entry->protocol, __entry->location)
+	TP_printk("skbaddr=%p protocol=%u location=%p reason: %s",
+		  __entry->skbaddr, __entry->protocol, __entry->location,
+		  __print_symbolic(__entry->reason,
+				   TRACE_SKB_DROP_REASON))
 );
 
 TRACE_EVENT(consume_skb,