linux-kernel - Re: [PATCH] bpf: remove unnecessary condition in bpf

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Message-ID: <20180709230059.p6afqogzp6rb4ka4@ast-mbp.dhcp.thefacebook.com>
Date:   Mon, 9 Jul 2018 16:01:01 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Tobias Tefke <tobias.tefke@...il.com>
Cc:     tobias.tefke@...anota.com, ast@...nel.org, daniel@...earbox.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: remove unnecessary condition in bpf_check()

On Mon, Jul 09, 2018 at 01:48:37PM +0200, Tobias Tefke wrote:
> In the label skip_full_check the function sanitize_dead_code()
> is being called if the return value equals zero.
> After that call there is another condition checking
> if the return value equals zero.
> If this condition evaluates to true,
> check_max_stack_depth() is being called.
> However, sanitize_dead_code() has no return value.
> Therefore the return value of bpf_check() is still the same
> and the condition can be removed.
> 
> Signed-off-by: Tobias Tefke <tobias.tefke@...anota.com>
> ---
>  kernel/bpf/verifier.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 9e2bf834f13a..b022d0a85427 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -5935,11 +5935,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
>  	while (!pop_stack(env, NULL, NULL));
>  	free_states(env);
>  
> -	if (ret == 0)
> +	if (ret == 0) {
>  		sanitize_dead_code(env);
> -
> -	if (ret == 0)
>  		ret = check_max_stack_depth(env);
> +	}

Technically the patch is correct, but I think it would make
the code harder to read. I prefer to keep it as-is.