netdev - Re: [PATCH 2/2] net: tcp: Add noinline_for_tracing annotation for tcp_drop

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Message-Id: <a4797bfc-73c3-44ca-bda2-8ad232d63d7e@app.fastmail.com>
Date: Thu, 24 Oct 2024 13:57:17 -0700
From: "Daniel Xu" <dxu@...uu.xyz>
To: "Yafang Shao" <laoar.shao@...il.com>,
 "Eric Dumazet" <edumazet@...gle.com>, "David Miller" <davem@...emloft.net>,
 dsahern@...nel.org, "Jakub Kicinski" <kuba@...nel.org>,
 "Paolo Abeni" <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, "Menglong Dong" <menglong8.dong@...il.com>
Subject: Re: [PATCH 2/2] net: tcp: Add noinline_for_tracing annotation for
 tcp_drop_reason()

Hi Yafang,

On Thu, Oct 24, 2024, at 2:37 AM, Yafang Shao wrote:
> We previously hooked the tcp_drop_reason() function using BPF to monitor
> TCP drop reasons. However, after upgrading our compiler from GCC 9 to GCC
> 11, tcp_drop_reason() is now inlined, preventing us from hooking into it.
> To address this, it would be beneficial to make noinline explicitly for
> tracing.

It looks like kfree_skb() tracepoint has rx_sk field now. Added in
c53795d48ee8 ("net: add rx_sk to trace_kfree_skb").

Between sk and skb, is there enough information to monitor TCP drops?
Or do you need something particular about tcp_drop_reason()?

Thanks,
Daniel