On Fri, Jul 15, 2016 at 11:08:10AM +0100, Mark Rutland wrote:
> In create_perf_stat_counter, when a target CPU has not been provided, we
> call __perf_evsel__open with empty_cpu_map, and open a single FD per
> thread. However, in read_counter we assume that we opened events for
> the product of threads and CPUs described in the evsel's cpu_map.
>
> Thus, if an evsel has a cpu_map with more than one entry, we will
> attempt to access FDs that we didn't open. This could result in a number
> of problems (e.g. blocking while reading from STDIN if the fd memory
> happened to be initialised to zero).
>
> This is problematic for systems were a logical CPU PMU covers some
> arbitrary subset of CPUs. The cpu_map of any evsel for that PMU will be
> initialised based on the cpumask exposed through sysfs, even if the user
> requests per-thread events.
>
> Signed-off-by: Mark Rutland <mark.rutl...@arm.com>
> Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
> Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: linux-kernel@vger.kernel.org
Acked-by: Jiri Olsa <jo...@kernel.org>
thanks,
jirka
> ---
> tools/perf/builtin-stat.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index ee7ada7..f3e21a2 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -276,8 +276,12 @@ perf_evsel__write_stat_event(struct perf_evsel *counter,
> u32 cpu, u32 thread,
> static int read_counter(struct perf_evsel *counter)
> {
> int nthreads = thread_map__nr(evsel_list->threads);
> - int ncpus = perf_evsel__nr_cpus(counter);
> - int cpu, thread;
> + int ncpus, cpu, thread;
> +
> + if (target__has_cpu(&target))
> + ncpus = perf_evsel__nr_cpus(counter);
> + else
> + ncpus = 1;
>
> if (!counter->supported)
> return -ENOENT;
> --
> 1.9.1
>
