[PATCH 1/2] perf stat: Fix segfault when counting armv8_pmu events

[Namhyung Kim]

On Wed, Sep 23, 2020 at 2:44 PM Jiri Olsa <jolsa at redhat.com> wrote:
>
> On Tue, Sep 22, 2020 at 11:13:45AM +0800, Wei Li wrote:
> > When executing perf stat with armv8_pmu events with a workload, it will
> > report a segfault as result.
>
> please share the perf stat command line you see that segfault for

It seems the description in the patch 0/2 already has it:

  [root at localhost hulk]# tools/perf/perf stat  -e
armv8_pmuv3_0/ll_cache_rd/,armv8_pmuv3_0/ll_cache_miss_rd/ ls >
/dev/null
  Segmentation fault

Thanks
Namhyun


>
> thanks,
> jirka
>
> >
> > (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 at 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 at entry=1, argv=0x30,
> >     argv at entry=0xfffffaea2f90, run_idx=119, run_idx at 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 at entry=0x9764b8 <commands+288>,
> >     argc=argc at entry=4, argv=argv at entry=0xfffffaea2f90) at perf.c:312
> > #7  0x00000000004bbb54 in handle_internal_command (argc=argc at entry=4,
> >     argv=argv at 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
> >
> > After debugging, i found the root reason is that the xyarray fd is created
> > by evsel__open_per_thread() ignoring the cpu passed in
> > create_perf_stat_counter(), while the evsel' cpumap is assigned as the
> > corresponding PMU's cpumap in __add_event(). Thus, the xyarray fd is created
> > with ncpus of dummy cpumap and an out of bounds 'cpu' index will be used in
> > perf_evsel__close_fd_cpu().
> >
> > To address this, add a flag to mark this situation and avoid using the
> > affinity technique when closing/enabling/disabling events.
> >
> > Fixes: 7736627b865d ("perf stat: Use affinity for closing file descriptors")
> > Fixes: 704e2f5b700d ("perf stat: Use affinity for enabling/disabling events")
> > Signed-off-by: Wei Li <liwei391 at huawei.com>
> > ---