linux-kernel - Re: [PATCH] perf script: fix crash when processing recorded stat data

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Date:   Sun, 20 Jan 2019 23:01:21 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Tony Jones <tonyj@...e.de>
Cc:     linux-perf-users@...r.kernel.org, acme@...nel.org,
        Jin Yao <yao.jin@...ux.intel.com>, ak@...ux.intel.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf script: fix crash when processing recorded stat data

On Sun, Jan 20, 2019 at 11:14:14AM -0800, Tony Jones wrote:
> While updating Perf to work with Python3 and Python2 I noticed that the 
> stat-cpi script was dumping core.
> 
> $ perf  stat -e cycles,instructions record -o /tmp/perf.data /bin/false
> 
>  Performance counter stats for '/bin/false':
> 
>            802,148      cycles
> 
>            604,622      instructions                                                       802,148      cycles
>            604,622      instructions
> 
>        0.001445842 seconds time elapsed
> 
> $ perf script -i /tmp/perf.data -s scripts/python/stat-cpi.py
> Segmentation fault (core dumped)
> ...
> ...
>     rblist=rblist@...ry=0xb2a200 <rt_stat>,
>     new_entry=new_entry@...ry=0x7ffcb755c310) at util/rblist.c:33
>     ctx=<optimized out>, type=<optimized out>, create=<optimized out>,
>     cpu=<optimized out>, evsel=<optimized out>) at util/stat-shadow.c:118
>     ctx=<optimized out>, type=<optimized out>, st=<optimized out>)
>     at util/stat-shadow.c:196
>     count=count@...ry=727442, cpu=cpu@...ry=0, st=0xb2a200 <rt_stat>)
>     at util/stat-shadow.c:239
>     config=config@...ry=0xafeb40 <stat_config>,
>     counter=counter@...ry=0x133c6e0) at util/stat.c:372
> ...
> ...
> 
> The issue is that since 1fcd03946b52 perf_stat__update_shadow_stats now calls
> update_runtime_stat passing rt_stat rather than calling update_stats but
> perf_stat__init_shadow_stats has never been called to initialize rt_stat in
> the script path processing recorded stat data.
> 
> Since I can't see any reason why perf_stat__init_shadow_stats() is presently
> initialized like it is in builtin-script.c::perf_sample__fprint_metric()
> [4bd1bef8bba2f] I'm proposing it instead be initialized once in __cmd_script
> 
> Fixes: 1fcd03946b52 ("perf stat: Update per-thread shadow stats")
> Signed-off-by: Tony Jones <tonyj@...e.de>
> ---
>  tools/perf/builtin-script.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> index d079f36d342d..9a6dd86e606f 100644
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -1681,13 +1681,8 @@ static void perf_sample__fprint_metric(struct perf_script *script,
>  		.force_header = false,
>  	};
>  	struct perf_evsel *ev2;
> -	static bool init;
>  	u64 val;
>  
> -	if (!init) {
> -		perf_stat__init_shadow_stats();
> -		init = true;
> -	}

well, there's no need to use shadow stats until stat
data is processed.. but it's actually just a static
initialization, so there's no need for late init

Reviewed-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka

>  	if (!evsel->stats)
>  		perf_evlist__alloc_stats(script->session->evlist, false);
>  	if (evsel_script(evsel->leader)->gnum++ == 0)
> @@ -2359,6 +2354,8 @@ static int __cmd_script(struct perf_script *script)
>  
>  	signal(SIGINT, sig_handler);
>  
> +	perf_stat__init_shadow_stats();
> +
>  	/* override event processing functions */
>  	if (script->show_task_events) {
>  		script->tool.comm = process_comm_event;
> -- 
> 2.18.0
>