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From:   Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date:   Fri, 6 Nov 2020 12:41:03 -0800
Message-ID: <CAEf4Bzan81+Go84k9fenKMixCthGzXZ6v27vTyqbkmBC1LLXyw@mail.gmail.com>
Subject: Re: [PATCH] trace: Fix passing zero to 'PTR_ERR' warning
To:     Wang Qing <wangqing@vivo.com>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Fri, Nov 6, 2020 at 12:49 AM Wang Qing <wangqing@vivo.com> wrote:
>
> Fix smatch warning.
>
> Signed-off-by: Wang Qing <wangqing@vivo.com>
> ---
>  kernel/trace/bpf_trace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 4517c8b..2cb9c45
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1198,7 +1198,7 @@ static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size,
>         *btf = bpf_get_btf_vmlinux();
>
>         if (IS_ERR_OR_NULL(*btf))
> -               return PTR_ERR(*btf);
> +               return PTR_ERR_OR_ZERO(*btf);

Either way returns zero for error? Which is the actual bug, so I think
the proper fix is:

return *btf ? PTR_ERR(*btf) : -EINVAL;

Or something like that.

>
>         if (ptr->type_id > 0)
>                 *btf_id = ptr->type_id;
> --
> 2.7.4
>