linux-kernel - Re: [PATCH bpf-next v3] bpf: Change value of MAX_TAIL_CALL

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Date:   Mon, 1 Nov 2021 16:44:51 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>,
        Johan Almbladh <johan.almbladh@...finetworks.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, illusionist.neo@...il.com,
        zlim.lnx@...il.com, naveen.n.rao@...ux.ibm.com,
        luke.r.nels@...il.com, xi.wang@...il.com, bjorn@...nel.org,
        iii@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        udknight@...il.com, davem@...emloft.net
Subject: Re: [PATCH bpf-next v3] bpf: Change value of MAX_TAIL_CALL_CNT from
 32 to 33

On 10/29/21 1:53 PM, Tiezhu Yang wrote:
[...]
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index b6c72af..6d10292 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -1565,7 +1565,8 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
>   
>   		if (unlikely(index >= array->map.max_entries))
>   			goto out;
> -		if (unlikely(tail_call_cnt > MAX_TAIL_CALL_CNT))
> +
> +		if (unlikely(tail_call_cnt == MAX_TAIL_CALL_CNT))
>   			goto out;
>   

Why making it less robust by going with == rather than >= ?