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From: Djalal Harouni <tixxdz@gmail.com>
To: tixxdz@gmail.com
Cc: Tejun Heo <tj@kernel.org>,
	Zefan Li <lizefan.x@bytedance.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	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>,
	Yonghong Song <yonghong.song@linux.dev>,
	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>,
	Mykola Lysenko <mykolal@fb.com>,
	Shuah Khan <shuah@kernel.org>,
	linux-kernel@vger.kernel.org,
	cgroups@vger.kernel.org,
	bpf@vger.kernel.org,
	linux-kselftest@vger.kernel.org
Subject: [RFC PATCH bpf-next 2/3] bpf: add bpf_task_freeze_cgroup() to freeze the cgroup of a task
Date: Wed, 27 Mar 2024 23:53:24 +0100
Message-Id: <20240327225334.58474-3-tixxdz@gmail.com>
In-Reply-To: <20240327225334.58474-1-tixxdz@gmail.com>
References: <20240327-ccb56fc7a6e80136db80876c@djalal>
 <20240327225334.58474-1-tixxdz@gmail.com>
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This patch adds a new bpf helper bpf_task_freeze_cgroup() to freeze a
cgroup of a task and all its descendant cgroups. It requires the task
to be on the default cgroup v2 hierarchy.

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.

This helper will acquire the cgroup_mutex during its operation and
release it before it returns.

Signed-off-by: Djalal Harouni <tixxdz@gmail.com>
---
 kernel/bpf/helpers.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 9234174ccb21..8d510a1b265c 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2270,6 +2270,36 @@ bpf_task_get_cgroup1(struct task_struct *task, int hierarchy_id)
 		return NULL;
 	return cgrp;
 }
+
+/**
+ * bpf_task_freeze_cgroup - Freeze the task cgroup and all its descendant cgroups.
+ *
+ * @task: The target task
+ * @freeze: freeze state, passing value 1 causes the freezing of the cgroup
+ * and all descendant cgroups. Processes under this cgroup hierarchy will
+ * be stopped and will not run until the cgroup is explicitly unfrozen.
+ * Passing value 0 unthaws the task cgroup and its descendant cgroups.
+ *
+ * Return: %0 on success or a negative errno code on failure.
+ */
+__bpf_kfunc int bpf_task_freeze_cgroup(struct task_struct *task, int freeze)
+{
+	int ret;
+	struct cgroup *cgrp;
+
+	rcu_read_lock();
+	cgrp = task_dfl_cgroup(task);
+	if (!cgrp || !cgroup_tryget(cgrp)) {
+		rcu_read_unlock();
+		return -ENOENT;
+	}
+	rcu_read_unlock();
+
+	ret = cgroup_freeze_no_kn(cgrp, freeze);
+	cgroup_put(cgrp);
+
+	return ret;
+}
 #endif /* CONFIG_CGROUPS */
 
 /**
@@ -2577,6 +2607,7 @@ BTF_ID_FLAGS(func, bpf_cgroup_ancestor, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_cgroup_from_id, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_under_cgroup, KF_RCU)
 BTF_ID_FLAGS(func, bpf_task_get_cgroup1, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_task_freeze_cgroup, KF_TRUSTED_ARGS | KF_SLEEPABLE)
 #endif
 BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_throw)
-- 
2.34.1