linux-kernel - Re: [PATCHv2 bpf-next 1/9] uprobe: Add support for session consumer

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Message-ID: <20240702130408.GH11386@noisy.programming.kicks-ass.net>
Date: Tue, 2 Jul 2024 15:04:08 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...omium.org>,
	Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCHv2 bpf-next 1/9] uprobe: Add support for session consumer

On Mon, Jul 01, 2024 at 06:41:07PM +0200, Jiri Olsa wrote:

> +static void
> +uprobe_consumer_account(struct uprobe *uprobe, struct uprobe_consumer *uc)
> +{
> +	static unsigned int session_id;
> +
> +	if (uc->session) {
> +		uprobe->sessions_cnt++;
> +		uc->session_id = ++session_id ?: ++session_id;
> +	}
> +}

The way I understand this code, you create a consumer every time you do
uprobe_register() and unregister makes it go away.

Now, register one, then 4g-1 times register+unregister, then register
again.

The above seems to then result in two consumers with the same
session_id, which leads to trouble.

Hmm?