On 7/1/19 3:32 PM, Andrii Nakryiko wrote:
> On Mon, Jul 1, 2019 at 10:16 AM Yonghong Song <yhs@xxxxxx> wrote:
>>
>>
>>
>> On 6/28/19 8:49 PM, Andrii Nakryiko wrote:
>>> Use new bpf_program__attach_perf_event() in test previously relying on
>>> direct ioctl manipulations.
>>>
>>> Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
>>> Reviewed-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
>>> Acked-by: Song Liu <songliubraving@xxxxxx>
>>> ---
>>> .../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.
Double checked again. You are correct. We do not have issues here.
>
>>
>>> close_prog:
>>> bpf_object__close(obj);
>>> }
>>>
