netdev - Re: [PATCH v3 bpf-next 2/4] bpf: introduce helper bpf_get_task

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Date:   Sat, 27 Jun 2020 13:35:55 -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>,
        Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH v3 bpf-next 2/4] bpf: introduce helper bpf_get_task_stack()

On Fri, Jun 26, 2020 at 5:29 PM Song Liu <songliubraving@...com> wrote:
>
> Introduce helper bpf_get_task_stack(), which dumps stack trace of given
> task. This is different to bpf_get_stack(), which gets stack track of
> current task. One potential use case of bpf_get_task_stack() is to call
> it from bpf_iter__task and dump all /proc/<pid>/stack to a seq_file.
>
> bpf_get_task_stack() uses stack_trace_save_tsk() instead of
> get_perf_callchain() for kernel stack. The benefit of this choice is that
> stack_trace_save_tsk() doesn't require changes in arch/. The downside of
> using stack_trace_save_tsk() is that stack_trace_save_tsk() dumps the
> stack trace to unsigned long array. For 32-bit systems, we need to
> translate it to u64 array.
>
> Acked-by: Andrii Nakryiko <andriin@...com>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  include/linux/bpf.h            |  1 +
>  include/uapi/linux/bpf.h       | 36 +++++++++++++++-
>  kernel/bpf/stackmap.c          | 75 ++++++++++++++++++++++++++++++++--
>  kernel/bpf/verifier.c          |  4 +-
>  kernel/trace/bpf_trace.c       |  2 +
>  scripts/bpf_helpers_doc.py     |  2 +
>  tools/include/uapi/linux/bpf.h | 36 +++++++++++++++-
>  7 files changed, 150 insertions(+), 6 deletions(-)
>

[...]

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 7de98906ddf4a..b608185e1ffd5 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -4864,7 +4864,9 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
>         if (err)
>                 return err;
>
> -       if (func_id == BPF_FUNC_get_stack && !env->prog->has_callchain_buf) {
> +       if ((func_id == BPF_FUNC_get_stack ||
> +            func_id == BPF_FUNC_get_task_stack) &&
> +           !env->prog->has_callchain_buf) {
>                 const char *err_str;
>

I'm glad it was so simple :) Thanks for checking!

[...]