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Subject[tip:perf/urgent] perf evsel: Fix attr.exclude_kernel setting for default cycles:p
Commit-ID:  f1e52f14a69386ac460a8d700df0647a631cf595
Gitweb: https://git.kernel.org/tip/f1e52f14a69386ac460a8d700df0647a631cf595
Author: Arnaldo Carvalho de Melo <acme@redhat.com>
AuthorDate: Fri, 22 Sep 2017 15:41:44 -0300
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Mon, 25 Sep 2017 10:39:45 -0300

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: d37a36979077 ("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>
---
tools/perf/util/evsel.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 4bb8937..0dccdb8 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -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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