linux-kernel - Re: [PATCH V2 bpf-next 1/2] bpf: add bpf_task_get

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Message-ID: <ZfhmsVTIe-khu9uP@google.com>
Date: Mon, 18 Mar 2024 09:07:13 -0700
From: Stanislav Fomichev <sdf@...gle.com>
To: Jose Fernandez <josef@...flix.com>
Cc: 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>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, Tycho Andersen <tycho@...ho.pizza>
Subject: Re: [PATCH V2 bpf-next 1/2] bpf: add bpf_task_get_cgroup kfunc

On 03/16, Jose Fernandez wrote:
> This patch enhances the BPF helpers by adding a kfunc to retrieve the
> cgroup v2 of a task, addressing a previous limitation where only
> bpf_task_get_cgroup1 was available for cgroup v1. The new kfunc is
> particularly useful for scenarios where obtaining the cgroup ID of a
> task other than the "current" one is necessary, which the existing
> bpf_get_current_cgroup_id helper cannot accommodate. A specific use
> case at Netflix involved the sched_switch tracepoint, where we had to
> get the cgroup IDs of both the prev and next tasks.
> 
> The bpf_task_get_cgroup kfunc acquires and returns a reference to a
> task's default cgroup, ensuring thread-safe access by correctly
> implementing RCU read locking and unlocking. It leverages the existing
> cgroup.h helper, and cgroup_tryget to safely acquire a reference to it.
> 
> Signed-off-by: Jose Fernandez <josef@...flix.com>
> Reviewed-by: Tycho Andersen <tycho@...ho.pizza>

Acked-by: Stanislav Fomichev <sdf@...gle.com>