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References: <20240311093526.1010158-1-dongmenglong.8@bytedance.com> <20240311093526.1010158-3-dongmenglong.8@bytedance.com>
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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Mon, 11 Mar 2024 18:48:58 -0700
Message-ID: <CAADnVQK57PziY+xdzW=d3HaG-bn87E3p9zf7thvmqV1t0iR4Yg@mail.gmail.com>
Subject: Re: [PATCH bpf-next v2 2/9] bpf: refactor the modules_array to ptr_array
To: Menglong Dong <dongmenglong.8@bytedance.com>
Cc: Andrii Nakryiko <andrii@kernel.org>, Alexei Starovoitov <ast@kernel.org>, 
	Daniel Borkmann <daniel@iogearbox.net>, Martin KaFai Lau <martin.lau@linux.dev>, Eddy Z <eddyz87@gmail.com>, 
	Song Liu <song@kernel.org>, Yonghong Song <yonghong.song@linux.dev>, 
	John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>, 
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, 
	Alexander Gordeev <agordeev@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, 
	Sven Schnelle <svens@linux.ibm.com>, "David S. Miller" <davem@davemloft.net>, 
	David Ahern <dsahern@kernel.org>, Dave Hansen <dave.hansen@linux.intel.com>, 
	X86 ML <x86@kernel.org>, Steven Rostedt <rostedt@goodmis.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Quentin Monnet <quentin@isovalent.com>, 
	bpf <bpf@vger.kernel.org>, 
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>, LKML <linux-kernel@vger.kernel.org>, 
	linux-riscv <linux-riscv@lists.infradead.org>, linux-s390 <linux-s390@vger.kernel.org>, 
	Network Development <netdev@vger.kernel.org>, linux-trace-kernel@vger.kernel.org, 
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On Mon, Mar 11, 2024 at 2:34=E2=80=AFAM 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 wher=
e
> 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 *ma=
p)
>  }
>  #endif
>
> +int bpf_add_ptr(struct ptr_array *arr, void *ptr)
> +{
> +       void **ptrs;
> +
> +       if (arr->cnt =3D=3D arr->cap) {
> +               arr->cap =3D max(16, arr->cap * 3 / 2);
> +               ptrs =3D krealloc_array(arr->ptrs, arr->cap, sizeof(*ptrs=
), GFP_KERNEL);
> +               if (!ptrs)
> +                       return -ENOMEM;
> +               arr->ptrs =3D ptrs;
> +       }
> +
> +       arr->ptrs[arr->cnt] =3D 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 =3D arr->cnt - 1; i >=3D 0; i--) {
> +               if (arr->ptrs[i] =3D=3D 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?