linux-kernel - Re: [PATCH v5 3/5] tracing/probes: Fix to update dynamic data counter if fetcharg uses it

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Date:   Thu, 13 Jul 2023 09:34:36 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     Dan Carpenter <dan.carpenter@...aro.org>,
        linux-trace-kernel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/5] tracing/probes: Fix to update dynamic data
 counter if fetcharg uses it

On Tue, 11 Jul 2023 23:15:48 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> Fix to update dynamic data counter ('dyndata') and max length ('maxlen')
> only if the fetcharg uses the dynamic data. Also get out arg->dynamic
> from unlikely(). This makes dynamic data address wrong if
> process_fetch_insn() returns error on !arg->dynamic case.
> 
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> Link: https://lore.kernel.org/all/20230710233400.5aaf024e@gandalf.local.home/
> Fixes: 9178412ddf5a ("tracing: probeevent: Return consumed bytes of dynamic area")
> Cc: stable@...r.kernel.org
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>

-- Steve

> ---
>  kernel/trace/trace_probe_tmpl.h |   12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/trace/trace_probe_tmpl.h b/kernel/trace/trace_probe_tmpl.h
> index ed9d57c6b041..185da001f4c3 100644
> --- a/kernel/trace/trace_probe_tmpl.h
> +++ b/kernel/trace/trace_probe_tmpl.h
> @@ -267,11 +267,13 @@ store_trace_args(void *data, struct trace_probe *tp, void *rec,
>  		if (unlikely(arg->dynamic))
>  			*dl = make_data_loc(maxlen, dyndata - base);
>  		ret = process_fetch_insn(arg->code, rec, dl, base);
> -		if (unlikely(ret < 0 && arg->dynamic)) {
> -			*dl = make_data_loc(0, dyndata - base);
> -		} else {
> -			dyndata += ret;
> -			maxlen -= ret;
> +		if (arg->dynamic) {
> +			if (unlikely(ret < 0)) {
> +				*dl = make_data_loc(0, dyndata - base);
> +			} else {
> +				dyndata += ret;
> +				maxlen -= ret;
> +			}
>  		}
>  	}
>  }