Subject: Re: [PATCH 06/14] bpf: Add bpf_kallsyms_tree tree

From: Jiri Olsa <[email-masked]>
Date: Wed, 12 Feb 2020 11:49:37 +0100

On Tue, Feb 11, 2020 at 10:21:10AM -0800, Andrii Nakryiko wrote:
> On Sat, Feb 8, 2020 at 7:43 AM Jiri Olsa <[email-masked]> 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 <[email-masked]>
> > ---
> >  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?

I followed the other latch tree ops functions and did not think
much about that.. will check

> 
> > +{
> > +       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?

right, should be bpf_ksym_tree_ops as you said

> 
> > +       .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?

right, thanks

jirka