On Mon, Jul 1, 2019 at 10:16 AM Yonghong Song [off-list ref] wrote:

On 6/28/19 8:49 PM, Andrii Nakryiko wrote:

quoted

Use new bpf_program__attach_perf_event() in test previously relying on
direct ioctl manipulations.

Signed-off-by: Andrii Nakryiko <redacted>
Reviewed-by: Stanislav Fomichev <redacted>
Acked-by: Song Liu <redacted>
---
  .../bpf/prog_tests/stacktrace_build_id_nmi.c  | 31 +++++++++----------
  1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/stacktrace_build_id_nmi.c b/tools/testing/selftests/bpf/prog_tests/stacktrace_build_id_nmi.c
index 1c1a2f75f3d8..9557b7dfb782 100644
--- a/tools/testing/selftests/bpf/prog_tests/stacktrace_build_id_nmi.c
+++ b/tools/testing/selftests/bpf/prog_tests/stacktrace_build_id_nmi.c

@@ -17,6 +17,7 @@ static __u64 read_perf_max_sample_freq(void)
  void test_stacktrace_build_id_nmi(void)
  {
      int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd;
+     const char *prog_name = "tracepoint/random/urandom_read";
      const char *file = "./test_stacktrace_build_id.o";
      int err, pmu_fd, prog_fd;
      struct perf_event_attr attr = {

@@ -25,7 +26,9 @@ void test_stacktrace_build_id_nmi(void)
              .config = PERF_COUNT_HW_CPU_CYCLES,
      };
      __u32 key, previous_key, val, duration = 0;
+     struct bpf_program *prog;
      struct bpf_object *obj;
+     struct bpf_link *link;
      char buf[256];
      int i, j;
      struct bpf_stack_build_id id_offs[PERF_MAX_STACK_DEPTH];

@@ -39,6 +42,10 @@ void test_stacktrace_build_id_nmi(void)
      if (CHECK(err, "prog_load", "err %d errno %d\n", err, errno))
              return;

+     prog = bpf_object__find_program_by_title(obj, prog_name);
+     if (CHECK(!prog, "find_prog", "prog '%s' not found\n", prog_name))
+             goto close_prog;
+
      pmu_fd = syscall(__NR_perf_event_open, &attr, -1 /* pid */,
                       0 /* cpu 0 */, -1 /* group id */,
                       0 /* flags */);

@@ -47,15 +54,12 @@ void test_stacktrace_build_id_nmi(void)
                pmu_fd, errno))
              goto close_prog;

-     err = ioctl(pmu_fd, PERF_EVENT_IOC_ENABLE, 0);
-     if (CHECK(err, "perf_event_ioc_enable", "err %d errno %d\n",
-               err, errno))
-             goto close_pmu;
-
-     err = ioctl(pmu_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
-     if (CHECK(err, "perf_event_ioc_set_bpf", "err %d errno %d\n",
-               err, errno))
-             goto disable_pmu;
+     link = bpf_program__attach_perf_event(prog, pmu_fd);
+     if (CHECK(IS_ERR(link), "attach_perf_event",
+               "err %ld\n", PTR_ERR(link))) {
+             close(pmu_fd);
+             goto close_prog;
+     }

      /* find map fds */
      control_map_fd = bpf_find_map(__func__, obj, "control_map");

@@ -134,8 +138,7 @@ void test_stacktrace_build_id_nmi(void)
       * try it one more time.
       */
      if (build_id_matches < 1 && retry--) {
-             ioctl(pmu_fd, PERF_EVENT_IOC_DISABLE);
-             close(pmu_fd);
+             bpf_link__destroy(link);
              bpf_object__close(obj);
              printf("%s:WARN:Didn't find expected build ID from the map, retrying\n",
                     __func__);

@@ -154,11 +157,7 @@ void test_stacktrace_build_id_nmi(void)
       */

  disable_pmu:
-     ioctl(pmu_fd, PERF_EVENT_IOC_DISABLE);
-
-close_pmu:
-     close(pmu_fd);
-
+     bpf_link__destroy(link);

There is a problem in bpf_link__destroy(link).
The "link = bpf_program__attach_perf_event(prog, pmu_fd)"
may be an error pointer (IS_ERR(link) is true), in which
case, link should be reset to NULL and then call
bpf_link__destroy(link). Otherwise, the program may
segfault or function incorrectly.

Not really, if bpf_program__attach_perf_event fails and IS_ERR(link)
is true, we'll close pmu_fd explicitly and `goto close_prog` bypassing
bpf_link__destroy. `goto disable_pmu` is done only after we
successfully established attached link.

So unless I still miss something, I think this will work reliably.

quoted

  close_prog:
      bpf_object__close(obj);
  }