Re: [PATCH] tracing/uprobe: Fix double perf_event linking on multiprobe uprobe

From: Peter Zijlstra <peterz@infradead.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: "Arnaldo Carvalho de Melo" <acme@kernel.org>,
	"Steven Rostedt" <rostedt@goodmis.org>,
	"Jiri Olsa" <jolsa@kernel.org>, "Ingo Molnar" <mingo@kernel.org>,
	"Naveen N . Rao" <naveen.n.rao@linux.ibm.com>,
	"Anil S Keshavamurthy" <anil.s.keshavamurthy@intel.com>,
	"David S . Miller" <davem@davemloft.net>,
	"Namhyung Kim" <namhyung@kernel.org>,
	"Toke Høiland-Jørgensen" <thoiland@redhat.com>,
	"Jean-Tsung Hsiao" <jhsiao@redhat.com>,
	"Jesper Dangaard Brouer" <brouer@redhat.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] tracing/uprobe: Fix double perf_event linking on multiprobe uprobe
Date: Mon, 20 Jan 2020 13:40:22 +0100	[thread overview]
Message-ID: <20200120124022.GA14897@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <157862073931.1800.3800576241181489174.stgit@devnote2>

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];
> +}