Commit f1e52f14 authored Sep 22, 2017 by Arnaldo Carvalho de Melo

perf evsel: Fix attr.exclude_kernel setting for default cycles:p



Yet another fix for probing the max attr.precise_ip setting: it is not
enough settting attr.exclude_kernel for !root users, as they _can_
profile the kernel if the kernel.perf_event_paranoid sysctl is set to
-1, so check that as well.

Testing it:

As non root:

  $ sysctl kernel.perf_event_paranoid
  kernel.perf_event_paranoid = 2
  $ perf record sleep 1
  $ perf evlist -v
  cycles:uppp: ..., exclude_kernel: 1, ... precise_ip: 3, ...

Now as non-root, but with kernel.perf_event_paranoid set set to the
most permissive value, -1:

  $ sysctl kernel.perf_event_paranoid
  kernel.perf_event_paranoid = -1
  $ perf record sleep 1
  $ perf evlist -v
  cycles:ppp: ..., exclude_kernel: 0, ... precise_ip: 3, ...
  $

I.e. non-root, default kernel.perf_event_paranoid: :uppp modifier = not allowed to sample the kernel,
     non-root, most permissible kernel.perf_event_paranoid: :ppp = allowed to sample the kernel.

In both cases, use the highest available precision: attr.precise_ip = 3.

Reported-and-Tested-by: Ingo Molnar <mingo@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: d37a3697 ("perf evsel: Fix attr.exclude_kernel setting for default cycles:p")
Link: http://lkml.kernel.org/n/tip-nj2qkf75xsd6pw6hhjzfqqdx@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

parent 549a3976

tools/perf/util/evsel.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -271,12 +271,17 @@ struct perf_evsel perf_evsel__new_idx(struct perf_event_attr attr, int idx)
		return evsel;
		}

		static bool perf_event_can_profile_kernel(void)
		{
		return geteuid() == 0 \|\| perf_event_paranoid() == -1;
		}

		struct perf_evsel *perf_evsel__new_cycles(bool precise)
		{
		struct perf_event_attr attr = {
		.type = PERF_TYPE_HARDWARE,
		.config = PERF_COUNT_HW_CPU_CYCLES,
		.exclude_kernel = geteuid() != 0,
		.exclude_kernel = !perf_event_can_profile_kernel(),
		};
		struct perf_evsel *evsel;

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