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perf stat: Balance opening and reading events

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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.rutland@arm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1468577293-19667-2-git-send-email-mark.rutland@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Mark Rutland 2016-07-15 11:08:10 +01:00 committed by Arnaldo Carvalho de Melo
parent ae3c14a028
commit 00e727bb38
1 changed files with 6 additions and 2 deletions
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8
tools/perf/builtin-stat.c
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@ -290,8 +290,12 @@ 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;