linux-kernel - Re: [PATCH v6 32/36] fprobe: Rewrite fprobe on function-graph tracer

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Date: Thu, 25 Jan 2024 16:11:51 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Florent Revest <revest@...omium.org>,
	linux-trace-kernel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>, bpf <bpf@...r.kernel.org>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Alan Maguire <alan.maguire@...cle.com>,
	Mark Rutland <mark.rutland@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, Guo Ren <guoren@...nel.org>
Subject: Re: [PATCH v6 32/36] fprobe: Rewrite fprobe on function-graph tracer

On Fri, Jan 12, 2024 at 07:17:06PM +0900, Masami Hiramatsu (Google) wrote:

SNIP

>   * Register @fp to ftrace for enabling the probe on the address given by @addrs.
> @@ -298,23 +547,27 @@ EXPORT_SYMBOL_GPL(register_fprobe);
>   */
>  int register_fprobe_ips(struct fprobe *fp, unsigned long *addrs, int num)
>  {
> -	int ret;
> -
> -	if (!fp || !addrs || num <= 0)
> -		return -EINVAL;
> -
> -	fprobe_init(fp);
> +	struct fprobe_hlist *hlist_array;
> +	int ret, i;
>  
> -	ret = ftrace_set_filter_ips(&fp->ops, addrs, num, 0, 0);
> +	ret = fprobe_init(fp, addrs, num);
>  	if (ret)
>  		return ret;
>  
> -	ret = fprobe_init_rethook(fp, num);
> -	if (!ret)
> -		ret = register_ftrace_function(&fp->ops);
> +	mutex_lock(&fprobe_mutex);
> +
> +	hlist_array = fp->hlist_array;
> +	ret = fprobe_graph_add_ips(addrs, num);

so fprobe_graph_add_ips registers the ftrace_ops and actually starts
the tracing.. and in the code below we prepare fprobe data that is
checked in the ftrace_ops callback.. should we do this this earlier
before calling fprobe_graph_add_ips/register_ftrace_graph?

jirka

> +	if (!ret) {
> +		add_fprobe_hash(fp);
> +		for (i = 0; i < hlist_array->size; i++)
> +			insert_fprobe_node(&hlist_array->array[i]);
> +	}
> +	mutex_unlock(&fprobe_mutex);
>  
>  	if (ret)
>  		fprobe_fail_cleanup(fp);
> +
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(register_fprobe_ips);
> @@ -352,14 +605,13 @@ EXPORT_SYMBOL_GPL(register_fprobe_syms);

SNIP