Re: [PATCH RFC v3 bpf-next 4/4] selftests/bpf: basic sleepable tests

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Jun 11, 2020 at 3:25 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> From: Alexei Starovoitov <ast@kernel.org>
>
> Modify few tests to sanity test sleepable bpf functionality.
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> Acked-by: KP Singh <kpsingh@google.com>
> ---
>  tools/testing/selftests/bpf/bench.c             |  2 ++
>  .../selftests/bpf/benchs/bench_trigger.c        | 17 +++++++++++++++++
>  tools/testing/selftests/bpf/progs/lsm.c         | 14 ++++++++++++--
>  .../testing/selftests/bpf/progs/trigger_bench.c |  7 +++++++
>  4 files changed, 38 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/bench.c b/tools/testing/selftests/bpf/bench.c
> index 944ad4721c83..1a427685a8a8 100644
> --- a/tools/testing/selftests/bpf/bench.c
> +++ b/tools/testing/selftests/bpf/bench.c
> @@ -317,6 +317,7 @@ extern const struct bench bench_trig_tp;
>  extern const struct bench bench_trig_rawtp;
>  extern const struct bench bench_trig_kprobe;
>  extern const struct bench bench_trig_fentry;
> +extern const struct bench bench_trig_fentry_sleep;
>  extern const struct bench bench_trig_fmodret;
>  extern const struct bench bench_rb_libbpf;
>  extern const struct bench bench_rb_custom;
> @@ -338,6 +339,7 @@ static const struct bench *benchs[] = {
>         &bench_trig_rawtp,
>         &bench_trig_kprobe,
>         &bench_trig_fentry,
> +       &bench_trig_fentry_sleep,

Can you please add results to commit description for fentry and
fentry_sleep benchmark, just for comparison?

>         &bench_trig_fmodret,
>         &bench_rb_libbpf,
>         &bench_rb_custom,

[...]

>
> @@ -28,6 +30,9 @@ int BPF_PROG(test_int_hook, struct vm_area_struct *vma,
>         is_stack = (vma->vm_start <= vma->vm_mm->start_stack &&
>                     vma->vm_end >= vma->vm_mm->start_stack);
>
> +       bpf_copy_from_user(args, sizeof(args), (void *)vma->vm_mm->arg_start);

is there some way to ensure that user memory definitely is not paged
in (and do it from user-space selftest part), so that
bpf_copy_from_user() *definitely* sleeps? That would be the real test.
As is, even bpf_probe_read_user() might succeed as well, isn't that
right?

Seems like doing madvise(MADV_DONTNEED) should be able to accomplish
that? So instead of reading arg_start, we can pre-setup mmap()'ed
file, MADV_DONTNEED it, then trigger LSM program and let it attempt
reading that chunk of memory?


> +       /*bpf_printk("args=%s\n", args);*/

debugging leftover?

> +
>         if (is_stack && monitored_pid == pid) {
>                 mprotect_count++;
>                 ret = -EPERM;
> @@ -36,7 +41,7 @@ int BPF_PROG(test_int_hook, struct vm_area_struct *vma,
>         return ret;
>  }
>
> -SEC("lsm/bprm_committed_creds")
> +SEC("lsm.s/bprm_committed_creds")
>  int BPF_PROG(test_void_hook, struct linux_binprm *bprm)
>  {
>         __u32 pid = bpf_get_current_pid_tgid() >> 32;
> @@ -46,3 +51,8 @@ int BPF_PROG(test_void_hook, struct linux_binprm *bprm)
>
>         return 0;
>  }

nit: empty line here, don't squash those functions together :)


> +SEC("lsm/task_free") /* lsm/ is ok, lsm.s/ fails */
> +int BPF_PROG(test_task_free, struct task_struct *task)
> +{
> +       return 0;
> +}
> diff --git a/tools/testing/selftests/bpf/progs/trigger_bench.c b/tools/testing/selftests/bpf/progs/trigger_bench.c
> index 8b36b6640e7e..9a4d09590b3d 100644
> --- a/tools/testing/selftests/bpf/progs/trigger_bench.c
> +++ b/tools/testing/selftests/bpf/progs/trigger_bench.c
> @@ -39,6 +39,13 @@ int bench_trigger_fentry(void *ctx)
>         return 0;
>  }
>
> +SEC("fentry.s/__x64_sys_getpgid")
> +int bench_trigger_fentry_sleep(void *ctx)
> +{
> +       __sync_add_and_fetch(&hits, 1);
> +       return 0;
> +}
> +
>  SEC("fmod_ret/__x64_sys_getpgid")
>  int bench_trigger_fmodret(void *ctx)
>  {
> --
> 2.23.0
>