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

[Feng Zhou]

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@xxxxxxxxxxxxx> wrote:
> > From: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
> >
> > test_progs:
> > Tests new ebpf helpers bpf_map_lookup_percpu_elem.
> >
> > Signed-off-by: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
> > ---
> >   .../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 ?


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