linux-kernel - Re: [PATCH] tracing/uprobe: Fix double perf

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Message-ID: <20200120124022.GA14897@hirez.programming.kicks-ass.net>
Date:   Mon, 20 Jan 2020 13:40:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Namhyung Kim <namhyung@...nel.org>,
        Toke Høiland-Jørgensen <thoiland@...hat.com>,
        Jean-Tsung Hsiao <jhsiao@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/uprobe: Fix double perf_event linking on
 multiprobe uprobe

On Fri, Jan 10, 2020 at 10:45:39AM +0900, Masami Hiramatsu wrote:

> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index 4ee703728aec..03e4e180058d 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -230,6 +230,7 @@ struct trace_probe_event {
>  	struct trace_event_call		call;
>  	struct list_head 		files;
>  	struct list_head		probes;
> +	char				data[0];
>  };

Would it make sense to make the above:

	struct trace_uprobe_filter	filter[0];

instead? That would ensure that alignment is respected. While I think
the current code works by accident.

> @@ -264,6 +263,14 @@ process_fetch_insn(struct fetch_insn *code, struct pt_regs *regs, void *dest,
>  }
>  NOKPROBE_SYMBOL(process_fetch_insn)
>  
> +static struct trace_uprobe_filter *
> +trace_uprobe_get_filter(struct trace_uprobe *tu)
> +{
> +	struct trace_probe_event *event = tu->tp.event;
> +
> +	return (struct trace_uprobe_filter *)&event->data[0];
> +}