Re: [PATCH v2 bpf-next 4/4] selftests/bpf: add bpf_iter test with bpf_get_task_stack()

[Song Liu]

> On Jun 26, 2020, at 1:21 PM, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
> 
> On Thu, Jun 25, 2020 at 5:15 PM Song Liu <songliubraving@xxxxxx> wrote:
>> 
>> The new test is similar to other bpf_iter tests.
>> 
>> Signed-off-by: Song Liu <songliubraving@xxxxxx>
>> ---
>> .../selftests/bpf/prog_tests/bpf_iter.c       | 17 ++++++
>> .../selftests/bpf/progs/bpf_iter_task_stack.c | 60 +++++++++++++++++++
>> 2 files changed, 77 insertions(+)
>> create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
>> 
>> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
>> index 87c29dde1cf96..baa83328f810d 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
>> @@ -5,6 +5,7 @@
>> #include "bpf_iter_netlink.skel.h"
>> #include "bpf_iter_bpf_map.skel.h"
>> #include "bpf_iter_task.skel.h"
>> +#include "bpf_iter_task_stack.skel.h"
>> #include "bpf_iter_task_file.skel.h"
>> #include "bpf_iter_test_kern1.skel.h"
>> #include "bpf_iter_test_kern2.skel.h"
>> @@ -106,6 +107,20 @@ static void test_task(void)
>>        bpf_iter_task__destroy(skel);
>> }
>> 
>> +static void test_task_stack(void)
>> +{
>> +       struct bpf_iter_task_stack *skel;
>> +
>> +       skel = bpf_iter_task_stack__open_and_load();
>> +       if (CHECK(!skel, "bpf_iter_task_stack__open_and_load",
>> +                 "skeleton open_and_load failed\n"))
>> +               return;
>> +
>> +       do_dummy_read(skel->progs.dump_task_stack);
>> +
>> +       bpf_iter_task_stack__destroy(skel);
>> +}
>> +
>> static void test_task_file(void)
>> {
>>        struct bpf_iter_task_file *skel;
>> @@ -392,6 +407,8 @@ void test_bpf_iter(void)
>>                test_bpf_map();
>>        if (test__start_subtest("task"))
>>                test_task();
>> +       if (test__start_subtest("task_stack"))
>> +               test_task_stack();
>>        if (test__start_subtest("task_file"))
>>                test_task_file();
>>        if (test__start_subtest("anon"))
>> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
>> new file mode 100644
>> index 0000000000000..83aca5b1a7965
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
>> @@ -0,0 +1,60 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2020 Facebook */
>> +/* "undefine" structs in vmlinux.h, because we "override" them below */
>> +#define bpf_iter_meta bpf_iter_meta___not_used
>> +#define bpf_iter__task bpf_iter__task___not_used
>> +#include "vmlinux.h"
>> +#undef bpf_iter_meta
>> +#undef bpf_iter__task
>> +#include <bpf/bpf_helpers.h>
>> +#include <bpf/bpf_tracing.h>
>> +
>> +char _license[] SEC("license") = "GPL";
>> +
>> +/* bpf_get_task_stack needs a stackmap to work */
> 
> no it doesn't anymore :) please drop

We still need stack_map_alloc() to call get_callchain_buffers() in this
case. Without an active stack map, get_callchain_buffers() may fail. 

Thanks,
Song