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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Tue, 25 Oct 2022 23:32:55 -0700
Message-ID: <CAADnVQ+Pe73yjys+fjW1TBPscCmv6K9ur5bDPr2056ejwBBdZg@mail.gmail.com>
Subject: Re: [PATCH bpf-next] bpf: Fix a typo in comment for DFS algorithm
To:     Xu Kuohai <xukuohai@huaweicloud.com>
Cc:     bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.fastabend@gmail.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        "David S . Miller" <davem@davemloft.net>
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On Tue, Oct 25, 2022 at 7:42 PM Xu Kuohai <xukuohai@huaweicloud.com> wrote:
>
> From: Xu Kuohai <xukuohai@huawei.com>
>
> There is a typo in comment for DFS algorithm in bpf/verifier.c. The top
> element should not be popped until all its neighbors have been checked.
> Fix it.
>
> Fixes: 475fb78fbf48 ("bpf: verifier (add branch/goto checks)")
> Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
> ---
>  kernel/bpf/verifier.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index b83a8d420520..96ba5ea6d1a6 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -10662,7 +10662,7 @@ static int check_return_code(struct bpf_verifier_env *env)
>   * 3      let S be a stack
>   * 4      S.push(v)
>   * 5      while S is not empty
> - * 6            t <- S.pop()
> + * 6            t <- S.top()

Even with this fix the comment is not quite accurate.
I wonder whether we should keep it or delete it completely.
At least please use 'peek' instead of 'top'.