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

[Andi Kleen]

> 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.

The flag seems like a hack. How about figuring out the correct number of 
CPUs and using that?

-Andi