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Date:   Fri, 26 Jun 2020 16:11:57 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...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 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?

>
> Thanks,
> Song

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