perf stat: Fix out of bounds CPU map access when handling armv8_pmu events

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 has confused which map
it should use when accessing file descriptors and this causes 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@entry=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@entry=1, argv=0x30,
      argv@entry=0xfffffaea2f90, run_idx=119, run_idx@entry=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@entry=0x9764b8 <commands+288>,
      argc=argc@entry=4, argv=argv@entry=0xfffffaea2f90) at perf.c:312
  #7  0x00000000004bbb54 in handle_internal_command (argc=argc@entry=4,
      argv=argv@entry=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).

Fixes: 7736627b86 ("perf stat: Use affinity for closing file descriptors")
Reported-by: Wei Li <liwei391@huawei.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Barry Song <song.bao.hua@hisilicon.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20201007081311.1831003-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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);