linux-kernel - Re: [PATCHv3 1/7] uprobe: Add support for session consumer

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Message-ID: <20240912163539.GE27648@redhat.com>
Date: Thu, 12 Sep 2024 18:35:39 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
	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: [PATCHv3 1/7] uprobe: Add support for session consumer

On 09/09, Jiri Olsa wrote:
>
>  handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs)
>  {
> +	struct return_consumer *ric = NULL;
>  	struct uprobe *uprobe = ri->uprobe;
>  	struct uprobe_consumer *uc;
> -	int srcu_idx;
> +	int srcu_idx, iter = 0;
>
>  	srcu_idx = srcu_read_lock(&uprobes_srcu);
>  	list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
>  				 srcu_read_lock_held(&uprobes_srcu)) {
> +		/*
> +		 * If we don't find return consumer, it means uprobe consumer
> +		 * was added after we hit uprobe and return consumer did not
> +		 * get registered in which case we call the ret_handler only
> +		 * if it's not session consumer.
> +		 */
> +		ric = return_consumer_find(ri, &iter, uc->id);
> +		if (!ric && uc->session)
> +			continue;
>  		if (uc->ret_handler)
> -			uc->ret_handler(uc, ri->func, regs);
> +			uc->ret_handler(uc, ri->func, regs, ric ? &ric->cookie : NULL);

So why do we need the new uc->session member and the uc->session above ?

If return_consumer_find() returns NULL, uc->ret_handler(..., NULL) can handle
this case itself?

Oleg.