[External] Re: [PATCH bpf-next v2 2/9] bpf: refactor the modules_array to ptr_array

[梦龙董]

On Tue, Mar 12, 2024 at 9:49 AM Alexei Starovoitov
<alexei.starovoitov at gmail.com> wrote:
>
> On Mon, Mar 11, 2024 at 2:34 AM Menglong Dong
> <dongmenglong.8 at bytedance.com> wrote:
> >
> > Refactor the struct modules_array to more general struct ptr_array, which
> > is used to store the pointers.
> >
> > Meanwhiles, introduce the bpf_try_add_ptr(), which checks the existing of
> > the ptr before adding it to the array.
> >
> > Seems it should be moved to another files in "lib", and I'm not sure where
> > to add it now, and let's move it to kernel/bpf/syscall.c for now.
> >
> > Signed-off-by: Menglong Dong <dongmenglong.8 at bytedance.com>
> > ---
> >  include/linux/bpf.h      | 10 +++++++++
> >  kernel/bpf/syscall.c     | 37 +++++++++++++++++++++++++++++++
> >  kernel/trace/bpf_trace.c | 48 ++++++----------------------------------
> >  3 files changed, 54 insertions(+), 41 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 0f677fdcfcc7..997765cdf474 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -304,6 +304,16 @@ struct bpf_map {
> >         s64 __percpu *elem_count;
> >  };
> >
> > +struct ptr_array {
> > +       void **ptrs;
> > +       int cnt;
> > +       int cap;
> > +};
> > +
> > +int bpf_add_ptr(struct ptr_array *arr, void *ptr);
> > +bool bpf_has_ptr(struct ptr_array *arr, struct module *mod);
> > +int bpf_try_add_ptr(struct ptr_array *arr, void *ptr);
> > +
> >  static inline const char *btf_field_type_name(enum btf_field_type type)
> >  {
> >         switch (type) {
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index f63f4da4db5e..4f230fd1f8e4 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -479,6 +479,43 @@ static void bpf_map_release_memcg(struct bpf_map *map)
> >  }
> >  #endif
> >
> > +int bpf_add_ptr(struct ptr_array *arr, void *ptr)
> > +{
> > +       void **ptrs;
> > +
> > +       if (arr->cnt == arr->cap) {
> > +               arr->cap = max(16, arr->cap * 3 / 2);
> > +               ptrs = krealloc_array(arr->ptrs, arr->cap, sizeof(*ptrs), GFP_KERNEL);
> > +               if (!ptrs)
> > +                       return -ENOMEM;
> > +               arr->ptrs = ptrs;
> > +       }
> > +
> > +       arr->ptrs[arr->cnt] = ptr;
> > +       arr->cnt++;
> > +       return 0;
> > +}
> > +
> > +bool bpf_has_ptr(struct ptr_array *arr, struct module *mod)
>
> Don't you need 'void *mod' here?
>

Oops, it should be void *ptr here, my mistake~

> > +{
> > +       int i;
> > +
> > +       for (i = arr->cnt - 1; i >= 0; i--) {
> > +               if (arr->ptrs[i] == mod)
> > +                       return true;
> > +       }
> > +       return false;
> > +}
>
> ...
>
> > -               kprobe_multi_put_modules(arr.mods, arr.mods_cnt);
> > -               kfree(arr.mods);
> > +               kprobe_multi_put_modules((struct module **)arr.ptrs, arr.cnt);
>
> Do you really need to type cast? Compiler doesn't convert void**
> automatically?

Yeah, the compiler reports errors without this casting.