netdev - Re: [PATCH 14/14] bpf: Sort bpf kallsyms symbols

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Date:   Tue, 11 Feb 2020 11:12:09 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Andrii Nakryiko <andriin@...com>, Yonghong Song <yhs@...com>,
        Song Liu <songliubraving@...com>,
        Martin KaFai Lau <kafai@...com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...hat.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>
Subject: Re: [PATCH 14/14] bpf: Sort bpf kallsyms symbols

On Sat, Feb 8, 2020 at 7:43 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Currently we don't sort bpf_kallsyms and display symbols
> in proc/kallsyms as they come in via __bpf_ksym_add.
>
> Using the latch tree to get the next bpf_ksym object
> and insert the new symbol ahead of it.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>

>  kernel/bpf/core.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 50af5dcf7ff9..c63ff34b2128 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -651,9 +651,30 @@ static struct latch_tree_root bpf_progs_tree __cacheline_aligned;
>
>  static void __bpf_ksym_add(struct bpf_ksym *ksym)
>  {
> +       struct list_head *head = &bpf_kallsyms;
> +
>         WARN_ON_ONCE(!list_empty(&ksym->lnode));
> -       list_add_tail_rcu(&ksym->lnode, &bpf_kallsyms);
>         latch_tree_insert(&ksym->tnode, &bpf_kallsyms_tree, &bpf_kallsyms_tree_ops);
> +
> +       /*
> +        * Add ksym into bpf_kallsyms in ordered position,
> +        * which is prepared for us by latch tree addition.
> +        *
> +        * Find out the next symbol and insert ksym right
> +        * ahead of it. If ksym is the last one, just tail
> +        * add to the bpf_kallsyms.
> +        */
> +       if (!list_empty(&bpf_kallsyms)) {

nit: this is a bit redundant check (and unlikely to be false)

> +               struct rb_node *next = rb_next(&ksym->tnode.node[0]);
> +
> +               if (next) {
> +                       struct bpf_ksym *ptr;
> +
> +                       ptr = container_of(next, struct bpf_ksym, tnode.node[0]);
> +                       head = &ptr->lnode;
> +               }
> +       }
> +       list_add_tail_rcu(&ksym->lnode, head);
>  }
>
>  void bpf_ksym_add(struct bpf_ksym *ksym)
> --
> 2.24.1
>