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

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Message-ID: <ZoQmkiKwsy41JNt4@krava>
Date: Tue, 2 Jul 2024 18:10:58 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Peter Zijlstra <peterz@...radead.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 Tue, Jul 02, 2024 at 03:04:08PM +0200, Peter Zijlstra wrote:
> 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?

ugh true.. will make it u64 :)

I think we could store uprobe_consumer pointer+ref in session_consumer,
and that would make the unregister path more interesting.. will check

thanks,
jirka