Date:   Fri, 13 May 2022 09:49:37 +0800
From:   Feng Zhou <zhoufeng.zf@...edance.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
        Dave Marchevsky <davemarchevsky@...com>,
        Joanne Koong <joannekoong@...com>,
        Geliang Tang <geliang.tang@...e.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        duanxiongchun@...edance.com,
        Muchun Song <songmuchun@...edance.com>,
        Dongdong Wang <wangdongdong.6@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        zhouchengming@...edance.com, yosryahmed@...gle.com
Subject: Re: [External] Re: [PATCH bpf-next v2 2/2] selftests/bpf: add test
 case for bpf_map_lookup_percpu_elem

在 2022/5/13 上午12:43, Andrii Nakryiko 写道:
> On Wed, May 11, 2022 at 8:58 PM Feng Zhou <zhoufeng.zf@...edance.com> wrote:
>> 在 2022/5/12 上午11:34, Andrii Nakryiko 写道:
>>> On Wed, May 11, 2022 at 2:39 AM Feng zhou <zhoufeng.zf@...edance.com> wrote:
>>>> From: Feng Zhou <zhoufeng.zf@...edance.com>
>>>>
>>>> test_progs:
>>>> Tests new ebpf helpers bpf_map_lookup_percpu_elem.
>>>>
>>>> Signed-off-by: Feng Zhou <zhoufeng.zf@...edance.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 //
>> Ok, I will do. Thanks.
>>
>>
>>>> +
>>>> +#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.
>>
>> Ok, I will do. Thanks.
>>
>>
>>>> +       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
>>
>> Ok, I will use 8 bytes for key and val. Thanks.
>>
>>
>>>> +       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
>>
>> Yes, sorry for my negligence.
>>
>>
>>>> +       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
>>
>> Good suggestion.
>>
>>
>>>> +
>>>> +       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 //
>>
>> Ok, I will do. Thanks.
>>
>>
>>>> +
>>>> +#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.
>>
>> Good suggestion. I check the code and find no bpf helper function to get
>> possible CPU nums.
>>
>> I think for the test function, read cpu0 elem value correctly should be
>> considered to be no problem.
>>
>> Or is it necessary to add a new helper function to get num_possible_cpus ?
>>
>>
> You can pass number of CPUs from user-space to BPF program through
> read-only variable (search for `const volatile` under progs/ for
> examples)
>
Ok, will do. Thanks.


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

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