linux-kernel - Re: [RFC PATCH bpf-next 0/3] bpf: freeze a task cgroup from bpf

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Date: Thu, 28 Mar 2024 07:22:05 -1000
From: Tejun Heo <tj@...nel.org>
To: Djalal Harouni <tixxdz@...il.com>
Cc: Zefan Li <lizefan.x@...edance.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	bpf@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH bpf-next 0/3] bpf: freeze a task cgroup from bpf

Hello, Djalal.

On Wed, Mar 27, 2024 at 11:53:22PM +0100, Djalal Harouni wrote:
> This patch series adds support to freeze the task cgroup hierarchy
> that is on a default cgroup v2 without going through kernfs interface.
> 
> For some cases we want to freeze the cgroup of a task based on some
> signals, doing so from bpf is better than user space which could be
> too late.
> 
> Planned users of this feature are: tetragon and systemd when freezing
> a cgroup hierarchy that could be a K8s pod, container, system service
> or a user session.
> 
> Patch 1: cgroup: add cgroup_freeze_no_kn() to freeze a cgroup from bpf
> Patch 2: bpf: add bpf_task_freeze_cgroup() to freeze the cgroup of a task
> Patch 3: selftests/bpf: add selftest for bpf_task_freeze_cgroup

It bothers me a bit that it's adding a dedicated interface for something
which already has a defined userspace interface. Would it be better to have
kfunc wrappers for kernel_read() and kernel_write()?

Thanks.

-- 
tejun