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Message-ID: <34832c57-644d-45d6-b4bc-bd801e8bc5f5@linux.dev>
Date: Mon, 18 Mar 2024 08:54:39 -0700
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Subject: Re: [PATCH V2 bpf-next 1/2] bpf: add bpf_task_get_cgroup kfunc
Content-Language: en-GB
To: Jose Fernandez <josef@netflix.com>, Alexei Starovoitov <ast@kernel.org>,
 Daniel Borkmann <daniel@iogearbox.net>, Andrii Nakryiko <andrii@kernel.org>,
 Martin KaFai Lau <martin.lau@linux.dev>, Eduard Zingerman
 <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
 John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>,
 Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
 Jiri Olsa <jolsa@kernel.org>
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-kselftest@vger.kernel.org, Tycho Andersen <tycho@tycho.pizza>
References: <20240316162241.628855-1-josef@netflix.com>
From: Yonghong Song <yonghong.song@linux.dev>
In-Reply-To: <20240316162241.628855-1-josef@netflix.com>
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On 3/16/24 9:22 AM, 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@netflix.com>
> Reviewed-by: Tycho Andersen <tycho@tycho.pizza>

Acked-by: Yonghong Song <yonghong.song@linux.dev>