core: add tracepoints for queueing skb to rcvbuf

This patch adds 2 tracepoints to get a status of a socket receive queue
and related parameter.

One tracepoint is added to sock_queue_rcv_skb. It records rcvbuf size
and its usage. The other tracepoint is added to __sk_mem_schedule and
it records limitations of memory for sockets and current usage.

By using these tracepoints we're able to know detailed reason why kernel
drop the packet.

Signed-off-by: Satoru Moriya <[e-mail]>
Acked-by: Neil Horman <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/trace/events/sock.h

···
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM sock
+
+#if !defined(_TRACE_SOCK_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SOCK_H
+
+#include <net/sock.h>
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(sock_rcvqueue_full,
+
+	TP_PROTO(struct sock *sk, struct sk_buff *skb),
+
+	TP_ARGS(sk, skb),
+
+	TP_STRUCT__entry(
+		__field(int, rmem_alloc)
+		__field(unsigned int, truesize)
+		__field(int, sk_rcvbuf)
+	),
+
+	TP_fast_assign(
+		__entry->rmem_alloc = atomic_read(&sk->sk_rmem_alloc);
+		__entry->truesize   = skb->truesize;
+		__entry->sk_rcvbuf  = sk->sk_rcvbuf;
+	),
+
+	TP_printk("rmem_alloc=%d truesize=%u sk_rcvbuf=%d",
+		__entry->rmem_alloc, __entry->truesize, __entry->sk_rcvbuf)
+);
+
+TRACE_EVENT(sock_exceed_buf_limit,
+
+	TP_PROTO(struct sock *sk, struct proto *prot, long allocated),
+
+	TP_ARGS(sk, prot, allocated),
+
+	TP_STRUCT__entry(
+		__array(char, name, 32)
+		__field(long *, sysctl_mem)
+		__field(long, allocated)
+		__field(int, sysctl_rmem)
+		__field(int, rmem_alloc)
+	),
+
+	TP_fast_assign(
+		strncpy(__entry->name, prot->name, 32);
+		__entry->sysctl_mem = prot->sysctl_mem;
+		__entry->allocated = allocated;
+		__entry->sysctl_rmem = prot->sysctl_rmem[0];
+		__entry->rmem_alloc = atomic_read(&sk->sk_rmem_alloc);
+	),
+
+	TP_printk("proto:%s sysctl_mem=%ld,%ld,%ld allocated=%ld "
+		"sysctl_rmem=%d rmem_alloc=%d",
+		__entry->name,
+		__entry->sysctl_mem[0],
+		__entry->sysctl_mem[1],
+		__entry->sysctl_mem[2],
+		__entry->allocated,
+		__entry->sysctl_rmem,
+		__entry->rmem_alloc)
+);
+
+#endif /* _TRACE_SOCK_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>

net/core/net-traces.c

···
 #include <trace/events/skb.h>
 #include <trace/events/net.h>
 #include <trace/events/napi.h>
+#include <trace/events/sock.h>
 #include <trace/events/udp.h>
 
 EXPORT_TRACEPOINT_SYMBOL_GPL(kfree_skb);

net/core/sock.c

···
 
 #include <linux/filter.h>
 
+#include <trace/events/sock.h>
+
 #ifdef CONFIG_INET
 #include <net/tcp.h>
 #endif
···
 	if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
 	    (unsigned)sk->sk_rcvbuf) {
 		atomic_inc(&sk->sk_drops);
+		trace_sock_rcvqueue_full(sk, skb);
 		return -ENOMEM;
 	}
 
···
 		if (sk->sk_wmem_queued + size >= sk->sk_sndbuf)
 			return 1;
 	}
+
+	trace_sock_exceed_buf_limit(sk, prot, allocated);
 
 	/* Alas. Undo changes. */
 	sk->sk_forward_alloc -= amt * SK_MEM_QUANTUM;