netdev - Re: [PATCH v2 net-next] tcp: add tracepoint trace_tcp_retransmit

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Date:   Mon, 30 Oct 2017 21:43:50 +0000
From:   Song Liu <songliubraving@...com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>
CC:     "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
        "liu.song.a23@...il.com" <liu.song.a23@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "hannes@...essinduktion.org" <hannes@...essinduktion.org>,
        "brendan.d.gregg@...il.com" <brendan.d.gregg@...il.com>,
        "ncardwell@...gle.com" <ncardwell@...gle.com>,
        David Ahern <dsahern@...il.com>,
        Kernel Team <Kernel-team@...com>,
        Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: [PATCH v2 net-next] tcp: add tracepoint
 trace_tcp_retransmit_synack()

CCing key audience of the patch.

Thanks,
Song

> On Oct 30, 2017, at 2:41 PM, Song Liu <songliubraving@...com> wrote:
> 
> This tracepoint can be used to trace synack retransmits. It maintains
> pointer to struct request_sock.
> 
> We cannot simply reuse trace_tcp_retransmit_skb() here, because the
> sk here is the LISTEN socket. The IP addresses and ports should be
> extracted from struct request_sock.
> 
> Note that, like many other tracepoints, this patch uses IS_ENABLED
> in TP_fast_assign macro, which triggers sparse warning like:
> 
> ./include/trace/events/tcp.h:274:1: error: directive in argument list
> ./include/trace/events/tcp.h:281:1: error: directive in argument list
> 
> However, there is no good solution to avoid these warnings. To the
> best of our knowledge, these warnings are harmless.
> 
> Signed-off-by: Song Liu <songliubraving@...com>
> Acked-by: Alexei Starovoitov <ast@...nel.org>
> Acked-by: Martin KaFai Lau <kafai@...com>
> ---
> include/trace/events/tcp.h | 56 ++++++++++++++++++++++++++++++++++++++++++++++
> net/ipv4/tcp_output.c      |  1 +
> 2 files changed, 57 insertions(+)
> 
> diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
> index 03699ba..07cccca 100644
> --- a/include/trace/events/tcp.h
> +++ b/include/trace/events/tcp.h
> @@ -237,6 +237,62 @@ TRACE_EVENT(tcp_set_state,
> 		  show_tcp_state_name(__entry->newstate))
> );
> 
> +TRACE_EVENT(tcp_retransmit_synack,
> +
> +	TP_PROTO(const struct sock *sk, const struct request_sock *req),
> +
> +	TP_ARGS(sk, req),
> +
> +	TP_STRUCT__entry(
> +		__field(const void *, skaddr)
> +		__field(const void *, req)
> +		__field(__u16, sport)
> +		__field(__u16, dport)
> +		__array(__u8, saddr, 4)
> +		__array(__u8, daddr, 4)
> +		__array(__u8, saddr_v6, 16)
> +		__array(__u8, daddr_v6, 16)
> +	),
> +
> +	TP_fast_assign(
> +		struct inet_request_sock *ireq = inet_rsk(req);
> +		struct in6_addr *pin6;
> +		__be32 *p32;
> +
> +		__entry->skaddr = sk;
> +		__entry->req = req;
> +
> +		__entry->sport = ireq->ir_num;
> +		__entry->dport = ntohs(ireq->ir_rmt_port);
> +
> +		p32 = (__be32 *) __entry->saddr;
> +		*p32 = ireq->ir_loc_addr;
> +
> +		p32 = (__be32 *) __entry->daddr;
> +		*p32 = ireq->ir_rmt_addr;
> +
> +#if IS_ENABLED(CONFIG_IPV6)
> +		if (sk->sk_family == AF_INET6) {
> +			pin6 = (struct in6_addr *)__entry->saddr_v6;
> +			*pin6 = ireq->ir_v6_loc_addr;
> +			pin6 = (struct in6_addr *)__entry->daddr_v6;
> +			*pin6 = ireq->ir_v6_rmt_addr;
> +		} else
> +#endif
> +		{
> +			pin6 = (struct in6_addr *)__entry->saddr_v6;
> +			ipv6_addr_set_v4mapped(ireq->ir_loc_addr, pin6);
> +			pin6 = (struct in6_addr *)__entry->daddr_v6;
> +			ipv6_addr_set_v4mapped(ireq->ir_rmt_addr, pin6);
> +		}
> +	),
> +
> +	TP_printk("sport=%hu dport=%hu saddr=%pI4 daddr=%pI4 saddrv6=%pI6c daddrv6=%pI6c",
> +		  __entry->sport, __entry->dport,
> +		  __entry->saddr, __entry->daddr,
> +		  __entry->saddr_v6, __entry->daddr_v6)
> +);
> +
> #endif /* _TRACE_TCP_H */
> 
> /* This part must be outside protection */
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index a69a34f..74d1c4d 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -3781,6 +3781,7 @@ int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
> 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
> 		if (unlikely(tcp_passive_fastopen(sk)))
> 			tcp_sk(sk)->total_retrans++;
> +		trace_tcp_retransmit_synack(sk, req);
> 	}
> 	return res;
> }
> -- 
> 2.9.5
>