netdev - Re: [PATCH bpf-next] bpf: trace jit code when enable BPF_JIT_ALWAYS

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Date:   Fri, 26 Mar 2021 07:24:33 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jianlin Lv <Jianlin.Lv@....com>
Cc:     bpf <bpf@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrey Ignatov <rdna@...com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Mahesh Bandewar <maheshb@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        iecedge@...il.com, nd <nd@....com>
Subject: Re: [PATCH bpf-next] bpf: trace jit code when enable BPF_JIT_ALWAYS_ON

On Fri, Mar 26, 2021 at 5:40 AM Jianlin Lv <Jianlin.Lv@....com> wrote:
>
> When CONFIG_BPF_JIT_ALWAYS_ON is enabled, the value of bpf_jit_enable in
> /proc/sys is limited to SYSCTL_ONE. This is not convenient for debugging.
> This patch modifies the value of extra2 (max) to 2 that support developers
> to emit traces on kernel log.
>
> Signed-off-by: Jianlin Lv <Jianlin.Lv@....com>
> ---
>  net/core/sysctl_net_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
> index d84c8a1b280e..aa16883ac445 100644
> --- a/net/core/sysctl_net_core.c
> +++ b/net/core/sysctl_net_core.c
> @@ -386,7 +386,7 @@ static struct ctl_table net_core_table[] = {
>                 .proc_handler   = proc_dointvec_minmax_bpf_enable,
>  # ifdef CONFIG_BPF_JIT_ALWAYS_ON
>                 .extra1         = SYSCTL_ONE,
> -               .extra2         = SYSCTL_ONE,
> +               .extra2         = &two,

"bpftool prog dump jited" is much better way to examine JITed dumps.
I'd rather remove bpf_jit_enable=2 altogether.