linux-kernel - Re: [PATCH v2 bpf-next 4/4] selftests/bpf: add bpf_iter test with bpf_get_task

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Date:   Fri, 26 Jun 2020 23:40:58 +0000
From:   Song Liu <songliubraving@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Peter Ziljstra <peterz@...radead.org>,
        "Alexei Starovoitov" <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Kernel Team" <Kernel-team@...com>,
        john fastabend <john.fastabend@...il.com>,
        "KP Singh" <kpsingh@...omium.org>
Subject: Re: [PATCH v2 bpf-next 4/4] selftests/bpf: add bpf_iter test with
 bpf_get_task_stack()



> On Jun 26, 2020, at 4:11 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> 
> On Fri, Jun 26, 2020 at 4:05 PM Song Liu <songliubraving@...com> wrote:
>> 
>> 
>> 
>>> On Jun 26, 2020, at 1:21 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
>>> 
>>> On Thu, Jun 25, 2020 at 5:15 PM Song Liu <songliubraving@...com> wrote:
>>>> 
>>>> The new test is similar to other bpf_iter tests.
>>>> 
>>>> Signed-off-by: Song Liu <songliubraving@...com>
>>>> ---
>>>> .../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.
> 
> Oh... um... is it possible to do it some other way? It's extremely
> confusing dependency. Does bpf_get_stack() also require stackmap?
> 

Aha, I thought bpf_get_stack() also requires stackmap, but it doesn't. 
The fix is in check_helper_call(). Let me do the same for bpf_get_task_stack(). 

Thanks,
Song