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

Alexei Starovoitov
2024-03-12T01:49:10Z

On Mon, Mar 11, 2024 at 2:34 AM Menglong Dong
<dongmenglong.8@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@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?

> +{
> + 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?