netdev - Re: [PATCH net-next 2/2] trace: tcp: fully support trace_tcp_send

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Message-ID: <20240311032717.GB1241282@maili.marvell.com>
Date: Mon, 11 Mar 2024 08:57:17 +0530
From: Ratheesh Kannoth <rkannoth@...vell.com>
To: Jason Xing <kerneljasonxing@...il.com>
CC: <edumazet@...gle.com>, <mhiramat@...nel.org>,
        <mathieu.desnoyers@...icios.com>, <rostedt@...dmis.org>,
        <kuba@...nel.org>, <pabeni@...hat.com>, <davem@...emloft.net>,
        <netdev@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>,
        Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next 2/2] trace: tcp: fully support
 trace_tcp_send_reset

On 2024-03-11 at 08:11:04, Jason Xing (kerneljasonxing@...il.com) wrote:
> From: Jason Xing <kernelxing@...cent.com>
>
> Prior to this patch, what we can see by enabling trace_tcp_send is
> only happening under two circumstances:
> 1) active rst mode
> 2) non-active rst mode and based on the full socket
>
> That means the inconsistency occurs if we use tcpdump and trace
> simultaneously to see how rst happens.
>
> It's necessary that we should take into other cases into considerations,
> say:
> 1) time-wait socket
> 2) no socket
> ...
>
> By parsing the incoming skb and reversing its 4-turple can
> we know the exact 'flow' which might not exist.
>
> Samples after applied this patch:
> 1. tcp_send_reset: skbaddr=XXX skaddr=XXX src=ip:port dest=ip:port
> state=TCP_ESTABLISHED
> 2. tcp_send_reset: skbaddr=000...000 skaddr=XXX src=ip:port dest=ip:port
> state=UNKNOWN
> Note:
> 1) UNKNOWN means we cannot extract the right information from skb.
> 2) skbaddr/skaddr could be 0
>
> Signed-off-by: Jason Xing <kernelxing@...cent.com>
> ---
>  include/trace/events/tcp.h | 39 ++++++++++++++++++++++++++++++++++++--
>  net/ipv4/tcp_ipv4.c        |  4 ++--
>  net/ipv6/tcp_ipv6.c        |  3 ++-
>  3 files changed, 41 insertions(+), 5 deletions(-)
>
> diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
> index 2495a1d579be..6c09d7941583 100644
> --- a/include/trace/events/tcp.h
> +++ b/include/trace/events/tcp.h
> @@ -107,11 +107,46 @@ DEFINE_EVENT(tcp_event_sk_skb, tcp_retransmit_skb,
>   * skb of trace_tcp_send_reset is the skb that caused RST. In case of
>   * active reset, skb should be NULL
>   */
> -DEFINE_EVENT(tcp_event_sk_skb, tcp_send_reset,
> +TRACE_EVENT(tcp_send_reset,
>
>  	TP_PROTO(const struct sock *sk, const struct sk_buff *skb),
>
> -	TP_ARGS(sk, skb)
> +	TP_ARGS(sk, skb),
> +
> +	TP_STRUCT__entry(
> +		__field(const void *, skbaddr)
> +		__field(const void *, skaddr)
> +		__field(int, state)
> +		__array(__u8, saddr, sizeof(struct sockaddr_in6))
> +		__array(__u8, daddr, sizeof(struct sockaddr_in6))
> +	),
> +
> +	TP_fast_assign(
> +		__entry->skbaddr = skb;
> +		__entry->skaddr = sk;
> +		/* Zero means unknown state. */
> +		__entry->state = sk ? sk->sk_state : 0;
> +
> +		memset(__entry->saddr, 0, sizeof(struct sockaddr_in6));
> +		memset(__entry->daddr, 0, sizeof(struct sockaddr_in6));
> +
> +		if (sk && sk_fullsock(sk)) {
> +			const struct inet_sock *inet = inet_sk(sk);
> +
> +			TP_STORE_ADDR_PORTS(__entry, inet, sk);
> +		} else {
> +			/*
> +			 * We should reverse the 4-turple of skb, so later
> +			 * it can print the right flow direction of rst.
> +			 */
> +			TP_STORE_ADDR_PORTS_SKB(skb, entry->daddr, entry->saddr);
> +		}
> +	),
> +
> +	TP_printk("skbaddr=%p skaddr=%p src=%pISpc dest=%pISpc state=%s",
Could you consider using %px ? is it permitted ? it will be easy to track skb.

> +		  __entry->skbaddr, __entry->skaddr,
> +		  __entry->saddr, __entry->daddr,
> +		  __entry->state ? show_tcp_state_name(__entry->state) : "UNKNOWN")
>  );
>
>  /*
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index a22ee5838751..d5c4a969c066 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -868,10 +868,10 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
>  	 */
>  	if (sk) {
>  		arg.bound_dev_if = sk->sk_bound_dev_if;
> -		if (sk_fullsock(sk))
> -			trace_tcp_send_reset(sk, skb);
>  	}
>
> +	trace_tcp_send_reset(sk, skb);
> +
>  	BUILD_BUG_ON(offsetof(struct sock, sk_bound_dev_if) !=
>  		     offsetof(struct inet_timewait_sock, tw_bound_dev_if));
>
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 3f4cba49e9ee..8e9c59b6c00c 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1113,7 +1113,6 @@ static void tcp_v6_send_reset(const struct sock *sk, struct sk_buff *skb)
>  	if (sk) {
>  		oif = sk->sk_bound_dev_if;
>  		if (sk_fullsock(sk)) {
> -			trace_tcp_send_reset(sk, skb);
>  			if (inet6_test_bit(REPFLOW, sk))
>  				label = ip6_flowlabel(ipv6h);
>  			priority = READ_ONCE(sk->sk_priority);
> @@ -1129,6 +1128,8 @@ static void tcp_v6_send_reset(const struct sock *sk, struct sk_buff *skb)
>  			label = ip6_flowlabel(ipv6h);
>  	}
>
> +	trace_tcp_send_reset(sk, skb);
> +
>  	tcp_v6_send_response(sk, skb, seq, ack_seq, 0, 0, 0, oif, 1,
>  			     ipv6_get_dsfield(ipv6h), label, priority, txhash,
>  			     &key);
> --
> 2.37.3
>