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

[Andi Kleen]

On Tue, Sep 22, 2020 at 12:23:21PM -0700, Andi Kleen wrote:
> > 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?

Also would like to understand what's different on ARM64 than other architectures.
Or could this happen on x86 too?

-Andi