linux-kernel - Re: [PATCH] perf stat: Fix segfault on armv8

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Date:   Wed, 7 Oct 2020 13:42:19 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Wei Li <liwei391@...wei.com>,
        Barry Song <song.bao.hua@...ilicon.com>
Subject: Re: [PATCH] perf stat: Fix segfault on armv8_pmu events

On Wed, Oct 07, 2020 at 05:13:11PM +0900, Namhyung Kim wrote:
> It was reported that perf stat crashed when using with armv8_pmu (cpu)
> events with the task mode.  As perf stat uses an empty cpu map for
> task mode but armv8_pmu has its own cpu mask, it confused which map
> should use when accessing file descriptors and caused segfaults:
> 
>   (gdb) bt
>   #0  0x0000000000603fc8 in perf_evsel__close_fd_cpu (evsel=<optimized out>,
>       cpu=<optimized out>) at evsel.c:122
>   #1  perf_evsel__close_cpu (evsel=evsel@...ry=0x716e950, cpu=7) at evsel.c:156
>   #2  0x00000000004d4718 in evlist__close (evlist=0x70a7cb0) at util/evlist.c:1242
>   #3  0x0000000000453404 in __run_perf_stat (argc=3, argc@...ry=1, argv=0x30,
>       argv@...ry=0xfffffaea2f90, run_idx=119, run_idx@...ry=1701998435)
>       at builtin-stat.c:929
>   #4  0x0000000000455058 in run_perf_stat (run_idx=1701998435, argv=0xfffffaea2f90,
>       argc=1) at builtin-stat.c:947
>   #5  cmd_stat (argc=1, argv=0xfffffaea2f90) at builtin-stat.c:2357
>   #6  0x00000000004bb888 in run_builtin (p=p@...ry=0x9764b8 <commands+288>,
>       argc=argc@...ry=4, argv=argv@...ry=0xfffffaea2f90) at perf.c:312
>   #7  0x00000000004bbb54 in handle_internal_command (argc=argc@...ry=4,
>       argv=argv@...ry=0xfffffaea2f90) at perf.c:364
>   #8  0x0000000000435378 in run_argv (argcp=<synthetic pointer>,
>       argv=<synthetic pointer>) at perf.c:408
>   #9  main (argc=4, argv=0xfffffaea2f90) at perf.c:538
> 
> To fix this, I simply used the given cpu map unless the evsel actually
> is not a system-wide event (like uncore events).
> 
> Reported-by: Wei Li <liwei391@...wei.com>
> Tested-by: Barry Song <song.bao.hua@...ilicon.com>
> Fixes: 7736627b865d ("perf stat: Use affinity for closing file descriptors")
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

Acked-by: Jiri Olsa <jolsa@...hat.com>

thanks,
jirka

> ---
>  tools/lib/perf/evlist.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
> index 2208444ecb44..cfcdbd7be066 100644
> --- a/tools/lib/perf/evlist.c
> +++ b/tools/lib/perf/evlist.c
> @@ -45,6 +45,9 @@ static void __perf_evlist__propagate_maps(struct perf_evlist *evlist,
>  	if (!evsel->own_cpus || evlist->has_user_cpus) {
>  		perf_cpu_map__put(evsel->cpus);
>  		evsel->cpus = perf_cpu_map__get(evlist->cpus);
> +	} else if (!evsel->system_wide && perf_cpu_map__empty(evlist->cpus)) {
> +		perf_cpu_map__put(evsel->cpus);
> +		evsel->cpus = perf_cpu_map__get(evlist->cpus);
>  	} else if (evsel->cpus != evsel->own_cpus) {
>  		perf_cpu_map__put(evsel->cpus);
>  		evsel->cpus = perf_cpu_map__get(evsel->own_cpus);
> -- 
> 2.28.0.806.g8561365e88-goog
>