linux-kernel - Re: [PATCH v4 net-next 1/7] net: add rx_sk to trace_kfree

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Date: Wed, 12 Jun 2024 09:59:43 +0200
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Yan Zhai <yan@...udflare.com>, netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 David Ahern <dsahern@...nel.org>,
 Abhishek Chauhan <quic_abchauha@...cinc.com>,
 Mina Almasry <almasrymina@...gle.com>, Florian Westphal <fw@...len.de>,
 Alexander Lobakin <aleksander.lobakin@...el.com>,
 David Howells <dhowells@...hat.com>, Jiri Pirko <jiri@...nulli.us>,
 Daniel Borkmann <daniel@...earbox.net>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Lorenzo Bianconi <lorenzo@...nel.org>,
 Pavel Begunkov <asml.silence@...il.com>, linux-kernel@...r.kernel.org,
 kernel-team@...udflare.com, Steven Rostedt <rostedt@...dmis.org>,
 Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Neil Horman <nhorman@...driver.com>, linux-trace-kernel@...r.kernel.org,
 Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH v4 net-next 1/7] net: add rx_sk to trace_kfree_skb

On 11/06/2024 22.11, Yan Zhai wrote:
> skb does not include enough information to find out receiving
> sockets/services and netns/containers on packet drops. In theory
> skb->dev tells about netns, but it can get cleared/reused, e.g. by TCP
> stack for OOO packet lookup. Similarly, skb->sk often identifies a local
> sender, and tells nothing about a receiver.
> 
> Allow passing an extra receiving socket to the tracepoint to improve
> the visibility on receiving drops.
> 
> Signed-off-by: Yan Zhai<yan@...udflare.com>
> ---
> v3->v4: adjusted the TP_STRUCT field order to be consistent
> v2->v3: fixed drop_monitor function prototype
> ---
>   include/trace/events/skb.h | 11 +++++++----
>   net/core/dev.c             |  2 +-
>   net/core/drop_monitor.c    |  9 ++++++---
>   net/core/skbuff.c          |  2 +-
>   4 files changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
> index 07e0715628ec..3e9ea1cca6f2 100644
> --- a/include/trace/events/skb.h
> +++ b/include/trace/events/skb.h
> @@ -24,13 +24,14 @@ DEFINE_DROP_REASON(FN, FN)
>   TRACE_EVENT(kfree_skb,
>   
>   	TP_PROTO(struct sk_buff *skb, void *location,
> -		 enum skb_drop_reason reason),
> +		 enum skb_drop_reason reason, struct sock *rx_sk),
>   
> -	TP_ARGS(skb, location, reason),
> +	TP_ARGS(skb, location, reason, rx_sk),
>   
>   	TP_STRUCT__entry(
>   		__field(void *,		skbaddr)
>   		__field(void *,		location)
> +		__field(void *,		rx_skaddr)

Is there any reason for appending the "addr" part to "rx_sk" ?
It makes it harder to read this is the sk (socket).

AFAICR the skbaddr naming is a legacy thing.

>   		__field(unsigned short,	protocol)
>   		__field(enum skb_drop_reason,	reason)
>   	),
> @@ -38,12 +39,14 @@ TRACE_EVENT(kfree_skb,
>   	TP_fast_assign(
>   		__entry->skbaddr = skb;
>   		__entry->location = location;
> +		__entry->rx_skaddr = rx_sk;
>   		__entry->protocol = ntohs(skb->protocol);
>   		__entry->reason = reason;
>   	),
>   
> -	TP_printk("skbaddr=%p protocol=%u location=%pS reason: %s",
> -		  __entry->skbaddr, __entry->protocol, __entry->location,
> +	TP_printk("skbaddr=%p rx_skaddr=%p protocol=%u location=%pS reason: %s",
                               ^^^^^^^^^
I find it hard to visually tell skbaddr and rx_skaddr apart.
And especially noticing the "skb" vs "sk" part of the string.

> +		  __entry->skbaddr, __entry->rx_skaddr, __entry->protocol,
> +		  __entry->location,
>   		  __print_symbolic(__entry->reason,
>   				   DEFINE_DROP_REASON(FN, FNe)))
>   );

--Jesper