skb: Add tracepoints to freeing skb

This patch adds tracepoint to consume_skb and add trace_kfree_skb
before __kfree_skb in skb_free_datagram_locked and net_tx_action.
Combinating with tracepoint on dev_hard_start_xmit, we can check
how long it takes to free transmitted packets. And using it, we can
calculate how many packets driver had at that time. It is useful when
a drop of transmitted packet is a problem.

sshd-6828 [000] 112689.258154: consume_skb: skbaddr=f2d99bb8

Signed-off-by: Koki Sanagi <[e-mail]>
Acked-by: David S. Miller <[e-mail]>
Acked-by: Neil Horman <[e-mail]>
Cc: Mathieu Desnoyers <[e-mail]>
Cc: Kaneshige Kenji <[e-mail]>
Cc: Izumo Taku <[e-mail]>
Cc: Kosaki Motohiro <[e-mail]>
Cc: Lai Jiangshan <[e-mail]>
Cc: Scott Mcmillan <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Eric Dumazet <[e-mail]>
LKML-Reference: <[e-mail]>
Signed-off-by: Frederic Weisbecker <[e-mail]>

include/trace/events/skb.h

···
 		__entry->skbaddr, __entry->protocol, __entry->location)
 );
 
+TRACE_EVENT(consume_skb,
+
+	TP_PROTO(struct sk_buff *skb),
+
+	TP_ARGS(skb),
+
+	TP_STRUCT__entry(
+		__field(	void *,	skbaddr	)
+	),
+
+	TP_fast_assign(
+		__entry->skbaddr = skb;
+	),
+
+	TP_printk("skbaddr=%p", __entry->skbaddr)
+);
+
 TRACE_EVENT(skb_copy_datagram_iovec,
 
 	TP_PROTO(const struct sk_buff *skb, int len),

net/core/datagram.c

···
 	unlock_sock_fast(sk, slow);
 
 	/* skb is now orphaned, can be freed outside of locked section */
+	trace_kfree_skb(skb, skb_free_datagram_locked);
 	__kfree_skb(skb);
 }
 EXPORT_SYMBOL(skb_free_datagram_locked);

net/core/dev.c

···
 #include <linux/random.h>
 #include <trace/events/napi.h>
 #include <trace/events/net.h>
+#include <trace/events/skb.h>
 #include <linux/pci.h>
 
 #include "net-sysfs.h"
···
 			clist = clist->next;
 
 			WARN_ON(atomic_read(&skb->users));
+			trace_kfree_skb(skb, net_tx_action);
 			__kfree_skb(skb);
 		}
 	}

net/core/skbuff.c

···
 		smp_rmb();
 	else if (likely(!atomic_dec_and_test(&skb->users)))
 		return;
+	trace_consume_skb(skb);
 	__kfree_skb(skb);
 }
 EXPORT_SYMBOL(consume_skb);