linux-kernel - Re: [PATCH] bpf: Remove unused field initialization

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Message-ID: <CAKH8qBuLhZ+T9fvP=DXeYevdrNofTPpEiQqq2RenBUKVghPmtA@mail.gmail.com>
Date:   Wed, 21 Dec 2022 12:10:08 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Daniel Borkmann <daniel@...earbox.net>,
        Hao Luo <haoluo@...gle.com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Song Liu <song@...nel.org>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: Remove unused field initialization

On Wed, Dec 21, 2022 at 11:55 AM Ricardo Ribalda <ribalda@...omium.org> wrote:
>
> Maxlen is used by standard proc_handlers such as proc_dointvec(), but in this
> case we have our own proc_handler. Remove the initialization.

Are you sure?

bpf_stats_handler
  proc_dointvec_minmax
    do_proc_dointvec
      __do_proc_dointvec
        vleft = table->maxlen / sizeof(*i);

Maybe we should really do the following instead?

.maxlen: sizeof(int)

?

> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
> bpf: Trivial remove of unitialised field.
>
> I have inspired myself in your code and heritaded this bug :). Fixing this
> here so none else makes the same mistake.
>
> To: Alexei Starovoitov <ast@...nel.org>
> To: Daniel Borkmann <daniel@...earbox.net>
> To: John Fastabend <john.fastabend@...il.com>
> To: Andrii Nakryiko <andrii@...nel.org>
> To: Martin KaFai Lau <martin.lau@...ux.dev>
> To: Song Liu <song@...nel.org>
> To: Yonghong Song <yhs@...com>
> To: KP Singh <kpsingh@...nel.org>
> To: Stanislav Fomichev <sdf@...gle.com>
> To: Hao Luo <haoluo@...gle.com>
> To: Jiri Olsa <jolsa@...nel.org>
> Cc: bpf@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  kernel/bpf/syscall.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 35972afb6850..8e55456bd648 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -5319,7 +5319,6 @@ static struct ctl_table bpf_syscall_table[] = {
>         {
>                 .procname       = "bpf_stats_enabled",
>                 .data           = &bpf_stats_enabled_key.key,
> -               .maxlen         = sizeof(bpf_stats_enabled_key),
>                 .mode           = 0644,
>                 .proc_handler   = bpf_stats_handler,
>         },
>
> ---
> base-commit: b6bb9676f2165d518b35ba3bea5f1fcfc0d969bf
> change-id: 20221221-bpf-syscall-58d1ac3f817a
>
> Best regards,
> --
> Ricardo Ribalda <ribalda@...omium.org>