Re: [bpf-next 2/2] selftests/bpf: add test cases for htab map

[Yonghong Song <yhs@meta.com>]

On 12/16/22 2:36 AM, Tonghao Zhang wrote:
> On Fri, Dec 16, 2022 at 12:10 PM Yonghong Song <yhs@meta.com> wrote:
>>
>>
>>
>> On 12/14/22 2:38 AM, xiangxia.m.yue@gmail.com wrote:
>>> From: Tonghao Zhang <xiangxia.m.yue@gmail.com>
>>>
>>> This testing show how to reproduce deadlock in special case.
>>>
>>> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
>>> Cc: Alexei Starovoitov <ast@kernel.org>
>>> Cc: Daniel Borkmann <daniel@iogearbox.net>
>>> Cc: Andrii Nakryiko <andrii@kernel.org>
>>> Cc: Martin KaFai Lau <martin.lau@linux.dev>
>>> Cc: Song Liu <song@kernel.org>
>>> Cc: Yonghong Song <yhs@fb.com>
>>> Cc: John Fastabend <john.fastabend@gmail.com>
>>> Cc: KP Singh <kpsingh@kernel.org>
>>> Cc: Stanislav Fomichev <sdf@google.com>
>>> Cc: Hao Luo <haoluo@google.com>
>>> Cc: Jiri Olsa <jolsa@kernel.org>
>>> Cc: Hou Tao <houtao1@huawei.com>
>>> ---
>>>    .../selftests/bpf/prog_tests/htab_deadlock.c  | 74 +++++++++++++++++++
>>>    .../selftests/bpf/progs/htab_deadlock.c       | 30 ++++++++
>>>    2 files changed, 104 insertions(+)
>>>    create mode 100644 tools/testing/selftests/bpf/prog_tests/htab_deadlock.c
>>>    create mode 100644 tools/testing/selftests/bpf/progs/htab_deadlock.c
>>>
>>> diff --git a/tools/testing/selftests/bpf/prog_tests/htab_deadlock.c b/tools/testing/selftests/bpf/prog_tests/htab_deadlock.c
>>> new file mode 100644
>>> index 000000000000..7dce4c2fe4f5
>>> --- /dev/null
>>> +++ b/tools/testing/selftests/bpf/prog_tests/htab_deadlock.c
>>> @@ -0,0 +1,74 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/* Copyright (c) 2022 DiDi Global Inc. */
>>> +#define _GNU_SOURCE
>>> +#include <pthread.h>
>>> +#include <sched.h>
>>> +#include <test_progs.h>
>>> +
>>> +#include "htab_deadlock.skel.h"
>>> +
>>> +static int perf_event_open(void)
>>> +{
>>> +     struct perf_event_attr attr = {0};
>>> +     int pfd;
>>> +
>>> +     /* create perf event */
>>> +     attr.size = sizeof(attr);
>>> +     attr.type = PERF_TYPE_HARDWARE;
>>> +     attr.config = PERF_COUNT_HW_CPU_CYCLES;
>>> +     attr.freq = 1;
>>> +     attr.sample_freq = 1000;
>>> +     pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
>>> +
>>> +     return pfd >= 0 ? pfd : -errno;
>>> +}
>>> +
>>> +void test_htab_deadlock(void)
>>> +{
>>> +     unsigned int val = 0, key = 20;
>>> +     struct bpf_link *link = NULL;
>>> +     struct htab_deadlock *skel;
>>> +     cpu_set_t cpus;
>>> +     int err;
>>> +     int pfd;
>>> +     int i;
>>
>> No need to have three lines for type 'int' variables. One line
>> is enough to hold all three variables.
>>
>>> +
>>> +     skel = htab_deadlock__open_and_load();
>>> +     if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
>>> +             return;
>>> +
>>> +     err = htab_deadlock__attach(skel);
>>> +     if (!ASSERT_OK(err, "skel_attach"))
>>> +             goto clean_skel;
>>> +
>>> +     /* NMI events. */
>>> +     pfd = perf_event_open();
>>> +     if (pfd < 0) {
>>> +             if (pfd == -ENOENT || pfd == -EOPNOTSUPP) {
>>> +                     printf("%s:SKIP:no PERF_COUNT_HW_CPU_CYCLES\n", __func__);
>>> +                     test__skip();
>>> +                     goto clean_skel;
>>> +             }
>>> +             if (!ASSERT_GE(pfd, 0, "perf_event_open"))
>>> +                     goto clean_skel;
>>> +     }
>>> +
>>> +     link = bpf_program__attach_perf_event(skel->progs.bpf_perf_event, pfd);
>>> +     if (!ASSERT_OK_PTR(link, "attach_perf_event"))
>>> +             goto clean_pfd;
>>> +
>>> +     /* Pinned on CPU 0 */
>>> +     CPU_ZERO(&cpus);
>>> +     CPU_SET(0, &cpus);
>>> +     pthread_setaffinity_np(pthread_self(), sizeof(cpus), &cpus);
>>> +
>>> +     for (i = 0; i < 100000; i++)
>>
>> Please add some comments in the above loop to mention the test
>> expects (hopefully) duriing one of bpf_map_update_elem(), one
>> perf event might kick to trigger prog bpf_nmi_handle run.
>>
>>> +             bpf_map_update_elem(bpf_map__fd(skel->maps.htab),
>>> +                                 &key, &val, BPF_ANY);
>>> +
>>> +     bpf_link__destroy(link);
>>> +clean_pfd:
>>> +     close(pfd);
>>> +clean_skel:
>>> +     htab_deadlock__destroy(skel);
>>> +}
>>> diff --git a/tools/testing/selftests/bpf/progs/htab_deadlock.c b/tools/testing/selftests/bpf/progs/htab_deadlock.c
>>> new file mode 100644
>>> index 000000000000..c4bd1567f882
>>> --- /dev/null
>>> +++ b/tools/testing/selftests/bpf/progs/htab_deadlock.c
>>> @@ -0,0 +1,30 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/* Copyright (c) 2022 DiDi Global Inc. */
>>> +#include <linux/bpf.h>
>>> +#include <bpf/bpf_helpers.h>
>>> +#include <bpf/bpf_tracing.h>
>>> +
>>> +char _license[] SEC("license") = "GPL";
>>> +
>>> +struct {
>>> +     __uint(type, BPF_MAP_TYPE_HASH);
>>> +     __uint(max_entries, 2);
>>> +     __uint(map_flags, BPF_F_ZERO_SEED);
>>> +     __uint(key_size, sizeof(unsigned int));
>>> +     __uint(value_size, sizeof(unsigned int));
>>> +} htab SEC(".maps");
>>
>> You can use
>>          __type(key, unsigned int);
>>          __type(value, unsigned int);
>> This is more expressive.
>>
>>> +
>>> +SEC("fentry/nmi_handle")
>>> +int bpf_nmi_handle(struct pt_regs *regs)
>>
>> Do we need this fentry function? Can be just put
>> bpf_map_update_elem() into bpf_perf_event program?
> Hi
> bpf_overflow_handler will check the bpf_prog_active, and
> bpf_map_update_value invokes bpf_disable_instrumentation,
> so the deadlock will not occur. In fentry/nmi_handle, bpf does not
> check the bpf_prog_active.

I see. Yes, fentry program does per prog recursion checking instead
of global bpf_prog_active.

> 
> Other comments look good to me, I will send v2 soon.
>> Also s390x and aarch64 failed the test due to none/incomplete trampoline
>> support. See bpf ci https://github.com/kernel-patches/bpf/pull/4211.
>> You need to add them in their corresponding deny list if this fentry
>> bpf program is used.
>>
>>> +{
>>> +     unsigned int val = 0, key = 4;
>>> +
>>> +     bpf_map_update_elem(&htab, &key, &val, BPF_ANY);
>>> +     return 0;
>>> +}
>>> +
>>> +SEC("perf_event")
>>> +int bpf_perf_event(struct pt_regs *regs)
>>> +{
>>> +     return 0;
>>> +}
> 
> 
>