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

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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 <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Wang Nan <[email protected]>
Fixes: d37a369790 ("perf evsel: Fix attr.exclude_kernel setting for default cycles:p")
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
This commit is contained in:
Arnaldo Carvalho de Melo 2017-09-22 15:41:44 -03:00
commit f1e52f14a6
1 changed files with 6 additions and 1 deletions
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7
tools/perf/util/evsel.c
View file

@ -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;