netdev - Re: [PATCH 06/14] bpf: Add bpf_kallsyms

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Date:   Tue, 11 Feb 2020 10:21:10 -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 06/14] bpf: Add bpf_kallsyms_tree tree

On Sat, Feb 8, 2020 at 7:43 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> The bpf_tree is used both for kallsyms iterations and searching
> for exception tables of bpf programs, which is needed only for
> bpf programs.
>
> Adding bpf_kallsyms_tree that will hold symbols for all bpf_prog,
> bpf_trampoline and bpf_dispatcher objects and keeping bpf_tree
> only for bpf_prog objects exception tables search to keep it fast.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  include/linux/bpf.h |  1 +
>  kernel/bpf/core.c   | 60 ++++++++++++++++++++++++++++++++++++++++-----
>  2 files changed, 55 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index da67ca3afa2f..151d7b1c8435 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -468,6 +468,7 @@ struct bpf_ksym {
>         unsigned long            end;
>         char                     name[KSYM_NAME_LEN];
>         struct list_head         lnode;
> +       struct latch_tree_node   tnode;
>  };
>
>  enum bpf_tramp_prog_type {
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index b9b7077e60f3..1daa72341450 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -606,8 +606,46 @@ static const struct latch_tree_ops bpf_tree_ops = {
>         .comp   = bpf_tree_comp,
>  };
>
> +static __always_inline unsigned long
> +bpf_get_ksym_start(struct latch_tree_node *n)

I thought static functions are never marked as inline in kernel
sources. Are there some special cases when its ok/necessary?

> +{
> +       const struct bpf_ksym *ksym;
> +
> +       ksym = container_of(n, struct bpf_ksym, tnode);
> +       return ksym->start;
> +}
> +
> +static __always_inline bool
> +bpf_ksym_tree_less(struct latch_tree_node *a,
> +                  struct latch_tree_node *b)
> +{
> +       return bpf_get_ksym_start(a) < bpf_get_ksym_start(b);
> +}
> +
> +static __always_inline int
> +bpf_ksym_tree_comp(void *key, struct latch_tree_node *n)
> +{
> +       unsigned long val = (unsigned long)key;
> +       const struct bpf_ksym *ksym;
> +
> +       ksym = container_of(n, struct bpf_ksym, tnode);
> +
> +       if (val < ksym->start)
> +               return -1;
> +       if (val >= ksym->end)
> +               return  1;
> +
> +       return 0;
> +}
> +
> +static const struct latch_tree_ops bpf_kallsyms_tree_ops = {

Given all the helper functions use bpf_ksym_tree and bpf_ksym
(bpf_ksym_find) prefixes, call this bpf_ksym_tree_ops?

> +       .less   = bpf_ksym_tree_less,
> +       .comp   = bpf_ksym_tree_comp,
> +};
> +
>  static DEFINE_SPINLOCK(bpf_lock);
>  static LIST_HEAD(bpf_kallsyms);
> +static struct latch_tree_root bpf_kallsyms_tree __cacheline_aligned;

same as above, bpf_ksym_tree for consistency?

>  static struct latch_tree_root bpf_tree __cacheline_aligned;
>
>  static void bpf_prog_ksym_node_add(struct bpf_prog_aux *aux)
> @@ -615,6 +653,7 @@ static void bpf_prog_ksym_node_add(struct bpf_prog_aux *aux)
>         WARN_ON_ONCE(!list_empty(&aux->ksym.lnode));
>         list_add_tail_rcu(&aux->ksym.lnode, &bpf_kallsyms);
>         latch_tree_insert(&aux->ksym_tnode, &bpf_tree, &bpf_tree_ops);
> +       latch_tree_insert(&aux->ksym.tnode, &bpf_kallsyms_tree, &bpf_kallsyms_tree_ops);
>  }
>

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