Re: [PATCHv2 bpf-next 3/4] bpf: Resolve symbols with kallsyms_lookup_names for kprobe multi link

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Apr 20, 2022 at 02:49:59PM -0700, Andrii Nakryiko wrote:
> On Mon, Apr 18, 2022 at 5:49 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Using kallsyms_lookup_names function to speed up symbols lookup in
> > kprobe multi link attachment and replacing with it the current
> > kprobe_multi_resolve_syms function.
> >
> > This speeds up bpftrace kprobe attachment:
> >
> >   # perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* {  } i:ms:1 { exit(); }'
> >   ...
> >   6.5681 +- 0.0225 seconds time elapsed  ( +-  0.34% )
> >
> > After:
> >
> >   # perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* {  } i:ms:1 { exit(); }'
> >   ...
> >   0.5661 +- 0.0275 seconds time elapsed  ( +-  4.85% )
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> 
> LGTM.
> 
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> 
> >  kernel/trace/bpf_trace.c | 113 +++++++++++++++++++++++----------------
> >  1 file changed, 67 insertions(+), 46 deletions(-)
> >
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index b26f3da943de..f49cdc46a21f 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -2226,6 +2226,60 @@ struct bpf_kprobe_multi_run_ctx {
> >         unsigned long entry_ip;
> >  };
> >
> > +struct user_syms {
> > +       const char **syms;
> > +       char *buf;
> > +};
> > +
> > +static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32 cnt)
> > +{
> > +       unsigned long __user usymbol;
> > +       const char **syms = NULL;
> > +       char *buf = NULL, *p;
> > +       int err = -EFAULT;
> > +       unsigned int i;
> > +
> > +       err = -ENOMEM;
> > +       syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
> > +       if (!syms)
> > +               goto error;
> > +
> > +       buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
> > +       if (!buf)
> > +               goto error;
> > +
> > +       for (p = buf, i = 0; i < cnt; i++) {
> > +               if (__get_user(usymbol, usyms + i)) {
> > +                       err = -EFAULT;
> > +                       goto error;
> > +               }
> > +               err = strncpy_from_user(p, (const char __user *) usymbol, KSYM_NAME_LEN);
> > +               if (err == KSYM_NAME_LEN)
> > +                       err = -E2BIG;
> > +               if (err < 0)
> > +                       goto error;
> > +               syms[i] = p;
> > +               p += err + 1;
> > +       }
> > +
> > +       err = 0;
> > +       us->syms = syms;
> > +       us->buf = buf;
> 
> return 0 here instead of falling through into error: block?

ok, will change

jirka

> 
> > +
> > +error:
> > +       if (err) {
> > +               kvfree(syms);
> > +               kvfree(buf);
> > +       }
> > +       return err;
> > +}
> > +
> > +static void free_user_syms(struct user_syms *us)
> > +{
> > +       kvfree(us->syms);
> > +       kvfree(us->buf);
> > +}
> > +
> >  static void bpf_kprobe_multi_link_release(struct bpf_link *link)
> >  {
> >         struct bpf_kprobe_multi_link *kmulti_link;
> 
> [...]