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>

3 files changed, 16 insertions, 9 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 83a4089990a0..84a0d9542fe9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4899,7 +4899,8 @@ static __latent_entropy void net_tx_action(struct softirq_action *h)
 			if (likely(get_kfree_skb_cb(skb)->reason == SKB_REASON_CONSUMED))
 				trace_consume_skb(skb);
 			else
-				trace_kfree_skb(skb, net_tx_action);
+				trace_kfree_skb(skb, net_tx_action,
+						SKB_DROP_REASON_NOT_SPECIFIED);
 
 			if (skb->fclone != SKB_FCLONE_UNAVAILABLE)
 				__kfree_skb(skb);
diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 3d0ab2eec916..7b288a121a41 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -110,7 +110,8 @@ static u32 net_dm_queue_len = 1000;
 
 struct net_dm_alert_ops {
 	void (*kfree_skb_probe)(void *ignore, struct sk_buff *skb,
-				void *location);
+				void *location,
+				enum skb_drop_reason reason);
 	void (*napi_poll_probe)(void *ignore, struct napi_struct *napi,
 				int work, int budget);
 	void (*work_item_func)(struct work_struct *work);
@@ -262,7 +263,9 @@ out:
 	spin_unlock_irqrestore(&data->lock, flags);
 }
 
-static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb, void *location)
+static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb,
+				void *location,
+				enum skb_drop_reason reason)
 {
 	trace_drop_common(skb, location);
 }
@@ -490,7 +493,8 @@ static const struct net_dm_alert_ops net_dm_alert_summary_ops = {
 
 static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
 					      struct sk_buff *skb,
-					      void *location)
+					      void *location,
+					      enum skb_drop_reason reason)
 {
 	ktime_t tstamp = ktime_get_real();
 	struct per_cpu_dm_data *data;
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index e514a36bcffc..0118f0afaa4f 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -759,21 +759,23 @@ void __kfree_skb(struct sk_buff *skb)
 EXPORT_SYMBOL(__kfree_skb);
 
 /**
- *	kfree_skb - free an sk_buff
+ *	kfree_skb_reason - free an sk_buff with special reason
  *	@skb: buffer to free
+ *	@reason: reason why this skb is dropped
  *
  *	Drop a reference to the buffer and free it if the usage count has
- *	hit zero.
+ *	hit zero. Meanwhile, pass the drop reason to 'kfree_skb'
+ *	tracepoint.
  */
-void kfree_skb(struct sk_buff *skb)
+void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
 {
 	if (!skb_unref(skb))
 		return;
 
-	trace_kfree_skb(skb, __builtin_return_address(0));
+	trace_kfree_skb(skb, __builtin_return_address(0), reason);
 	__kfree_skb(skb);
 }
-EXPORT_SYMBOL(kfree_skb);
+EXPORT_SYMBOL(kfree_skb_reason);
 
 void kfree_skb_list(struct sk_buff *segs)
 {