Re: [PATCH bpf-next v2 2/2] selftests/bpf: add test case for bpf_map_lookup_percpu_elem

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

On Wed, May 11, 2022 at 2:39 AM Feng zhou <zhoufeng.zf@bytedance.com> wrote:
>
> From: Feng Zhou <zhoufeng.zf@bytedance.com>
>
> test_progs:
> Tests new ebpf helpers bpf_map_lookup_percpu_elem.
>
> Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
> ---
>  .../bpf/prog_tests/map_lookup_percpu_elem.c   | 46 ++++++++++++++++
>  .../bpf/progs/test_map_lookup_percpu_elem.c   | 54 +++++++++++++++++++
>  2 files changed, 100 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/map_lookup_percpu_elem.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_map_lookup_percpu_elem.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/map_lookup_percpu_elem.c b/tools/testing/selftests/bpf/prog_tests/map_lookup_percpu_elem.c
> new file mode 100644
> index 000000000000..58b24c2112b0
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/map_lookup_percpu_elem.c
> @@ -0,0 +1,46 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2022 Bytedance

/* */ instead of //

> +
> +#include <test_progs.h>
> +
> +#include "test_map_lookup_percpu_elem.skel.h"
> +
> +#define TEST_VALUE  1
> +
> +void test_map_lookup_percpu_elem(void)
> +{
> +       struct test_map_lookup_percpu_elem *skel;
> +       int key = 0, ret;
> +       int nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);

I think this is actually wrong and will break selftests on systems
with offline CPUs. Please use libbpf_num_possible_cpus() instead.

> +       int *buf;
> +
> +       buf = (int *)malloc(nr_cpus*sizeof(int));
> +       if (!ASSERT_OK_PTR(buf, "malloc"))
> +               return;
> +       memset(buf, 0, nr_cpus*sizeof(int));

this is wrong, kernel expects to have roundup(sz, 8) per each CPU,
while you have just 4 bytes per each element

please also have spaces around multiplication operator here and above

> +       buf[0] = TEST_VALUE;
> +
> +       skel = test_map_lookup_percpu_elem__open_and_load();
> +       if (!ASSERT_OK_PTR(skel, "test_map_lookup_percpu_elem__open_and_load"))
> +               return;

buf leaking here

> +       ret = test_map_lookup_percpu_elem__attach(skel);
> +       ASSERT_OK(ret, "test_map_lookup_percpu_elem__attach");
> +
> +       ret = bpf_map_update_elem(bpf_map__fd(skel->maps.percpu_array_map), &key, buf, 0);
> +       ASSERT_OK(ret, "percpu_array_map update");
> +
> +       ret = bpf_map_update_elem(bpf_map__fd(skel->maps.percpu_hash_map), &key, buf, 0);
> +       ASSERT_OK(ret, "percpu_hash_map update");
> +
> +       ret = bpf_map_update_elem(bpf_map__fd(skel->maps.percpu_lru_hash_map), &key, buf, 0);
> +       ASSERT_OK(ret, "percpu_lru_hash_map update");
> +
> +       syscall(__NR_getuid);
> +
> +       ret = skel->bss->percpu_array_elem_val == TEST_VALUE &&
> +             skel->bss->percpu_hash_elem_val == TEST_VALUE &&
> +             skel->bss->percpu_lru_hash_elem_val == TEST_VALUE;
> +       ASSERT_OK(!ret, "bpf_map_lookup_percpu_elem success");

this would be better done as three separate ASSERT_EQ(), combining
into opaque true/false isn't helpful if something breaks

> +
> +       test_map_lookup_percpu_elem__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_map_lookup_percpu_elem.c b/tools/testing/selftests/bpf/progs/test_map_lookup_percpu_elem.c
> new file mode 100644
> index 000000000000..5d4ef86cbf48
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_map_lookup_percpu_elem.c
> @@ -0,0 +1,54 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2022 Bytedance

/* */ instead of //

> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +
> +int percpu_array_elem_val = 0;
> +int percpu_hash_elem_val = 0;
> +int percpu_lru_hash_elem_val = 0;
> +
> +struct {
> +       __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
> +       __uint(max_entries, 1);
> +       __type(key, __u32);
> +       __type(value, __u32);
> +} percpu_array_map SEC(".maps");
> +
> +struct {
> +       __uint(type, BPF_MAP_TYPE_PERCPU_HASH);
> +       __uint(max_entries, 1);
> +       __type(key, __u32);
> +       __type(value, __u32);
> +} percpu_hash_map SEC(".maps");
> +
> +struct {
> +       __uint(type, BPF_MAP_TYPE_LRU_PERCPU_HASH);
> +       __uint(max_entries, 1);
> +       __type(key, __u32);
> +       __type(value, __u32);
> +} percpu_lru_hash_map SEC(".maps");
> +
> +SEC("tp/syscalls/sys_enter_getuid")
> +int sysenter_getuid(const void *ctx)
> +{
> +       __u32 key = 0;
> +       __u32 cpu = 0;
> +       __u32 *value;
> +
> +       value = bpf_map_lookup_percpu_elem(&percpu_array_map, &key, cpu);
> +       if (value)
> +               percpu_array_elem_val = *value;
> +
> +       value = bpf_map_lookup_percpu_elem(&percpu_hash_map, &key, cpu);
> +       if (value)
> +               percpu_hash_elem_val = *value;
> +
> +       value = bpf_map_lookup_percpu_elem(&percpu_lru_hash_map, &key, cpu);
> +       if (value)
> +               percpu_lru_hash_elem_val = *value;
> +

if the test happens to run on CPU 0 then the test doesn't really test
much. It would be more interesting to have a bpf_loop() iteration that
would fetch values on each possible CPU instead and do something with
it.

> +       return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.20.1
>