netdev - Re: [PATCH RFC net-next 1/2] net: Reference bpf_redirect_info via task_struct on PREEMPT

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Message-ID: <20240214121921.VJJ2bCBE@linutronix.de>
Date: Wed, 14 Feb 2024 13:19:21 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Jesper Dangaard Brouer <hawk@...nel.org>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org,
	Björn Töpel <bjorn@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	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>,
	Jakub Kicinski <kuba@...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>,
	Peter Zijlstra <peterz@...radead.org>, Song Liu <song@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yonghong Song <yonghong.song@...ux.dev>
Subject: Re: [PATCH RFC net-next 1/2] net: Reference bpf_redirect_info via
 task_struct on PREEMPT_RT.

On 2024-02-13 21:50:51 [+0100], Jesper Dangaard Brouer wrote:
> I generally like the idea around bpf_xdp_storage.
> 
> I only skimmed the code, but noticed some extra if-statements (for
> !NULL). I don't think they will make a difference, but I know Toke want
> me to test it...

I've been looking at the assembly for the return value of
bpf_redirect_info() and there is a NULL pointer check. I hoped it was
obvious to be nun-NULL because it is a static struct.

Should this become a problem I could add
"__attribute__((returns_nonnull))" to the declaration of the function
which will optimize the NULL check away.

> I'll hopefully have time to look at code closer tomorrow.
> 
> --Jesper

Sebastian