linux-kernel - Re: [PATCH bpf-next v1 4/9] bpf: Introduce sleepable tracepoints

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Date:   Wed, 2 Mar 2022 11:41:41 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Hao Luo <haoluo@...gle.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Joe Burton <jevburton.kernel@...il.com>,
        Tejun Heo <tj@...nel.org>, joshdon@...gle.com, sdf@...gle.com,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v1 4/9] bpf: Introduce sleepable tracepoints

On Fri, Feb 25, 2022 at 03:43:34PM -0800, Hao Luo wrote:
> diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
> index e7c2276be33e..c73c7ab3680e 100644
> --- a/include/linux/tracepoint-defs.h
> +++ b/include/linux/tracepoint-defs.h
> @@ -51,6 +51,7 @@ struct bpf_raw_event_map {
>  	void			*bpf_func;
>  	u32			num_args;
>  	u32			writable_size;
> +	u32			sleepable;

It increases the size for all tracepoints. 
See BPF_RAW_TP in include/asm-generic/vmlinux.lds.h
Please switch writeable_size and sleepable to u16.
>  
> -static const struct bpf_func_proto *
> -syscall_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> +/* Syscall helpers that are also allowed in sleepable tracing prog. */
> +const struct bpf_func_proto *
> +tracing_prog_syscall_func_proto(enum bpf_func_id func_id,
> +				const struct bpf_prog *prog)
>  {
>  	switch (func_id) {
>  	case BPF_FUNC_sys_bpf:
>  		return &bpf_sys_bpf_proto;
> -	case BPF_FUNC_btf_find_by_name_kind:
> -		return &bpf_btf_find_by_name_kind_proto;
>  	case BPF_FUNC_sys_close:
>  		return &bpf_sys_close_proto;
> -	case BPF_FUNC_kallsyms_lookup_name:
> -		return &bpf_kallsyms_lookup_name_proto;
>  	case BPF_FUNC_mkdir:
>  		return &bpf_mkdir_proto;
>  	case BPF_FUNC_rmdir:
>  		return &bpf_rmdir_proto;
>  	case BPF_FUNC_unlink:
>  		return &bpf_unlink_proto;
> +	default:
> +		return NULL;
> +	}
> +}

If I read this correctly the goal is to disallow find_by_name_kind
and lookup_name from sleepable tps. Why? What's the harm?