netdev - Re: [PATCH bpf-next] net: Add a warning if NAPI cb missed xdp_do

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Date: Wed, 4 Oct 2023 07:09:26 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, "David S. Miller"
 <davem@...emloft.net>, Björn Töpel <bjorn@...nel.org>,
 Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Eric Dumazet <edumazet@...gle.com>,
 Hao Luo <haoluo@...gle.com>, Jesper Dangaard Brouer <hawk@...nel.org>, Jiri
 Olsa <jolsa@...nel.org>, John Fastabend <john.fastabend@...il.com>,
 Jonathan Lemon <jonathan.lemon@...il.com>, KP Singh <kpsingh@...nel.org>,
 Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Magnus Karlsson
 <magnus.karlsson@...el.com>, Martin KaFai Lau <martin.lau@...ux.dev>, Paolo
 Abeni <pabeni@...hat.com>, Song Liu <song@...nel.org>, Stanislav Fomichev
 <sdf@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, Yonghong Song
 <yonghong.song@...ux.dev>
Subject: Re: [PATCH bpf-next] net: Add a warning if NAPI cb missed
 xdp_do_flush().

On Fri, 29 Sep 2023 18:58:25 +0200 Sebastian Andrzej Siewior wrote:
> +#if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_DEBUG_NET)
> +bool __dev_check_flush(void);
> +bool __cpu_map_check_flush(void);
> +
> +#else
> +static inline bool __dev_check_flush(void)
> +{
> +	return false;
> +}
> +
> +static inline bool __cpu_map_check_flush(void)
> +{
> +	return false;
> +}
> +#endif

I think you're going too hard with the ifdefs.
These functions are only called if DEBUG_NET, add if BPF on the call
site and spare us the static inlines for all the __ helpers.

>  static __always_inline int
>  bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr)
>  {
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 27406aee2d402..db095d731813e 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -1025,6 +1025,14 @@ int xdp_do_redirect_frame(struct net_device *dev,
>  			  struct bpf_prog *prog);
>  void xdp_do_flush(void);
>  
> +#ifdef CONFIG_DEBUG_NET
> +void xdp_do_check_flushed(struct napi_struct *napi);
> +
> +#else
> +static inline void xdp_do_check_flushed(struct napi_struct *napi) { }
> +
> +#endif

Can you move this to net/core/dev.h? Or a new header under net/core
if you prefer? This looks internal to the stack.
Also nit: drop the empty lines inside the #ifdef?