linux-kernel - Re: [PATCH V2 bpf-next 2/2] selftests/bpf: add selftest for bpf_task_get

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Message-ID: <ZfgQXlU_wKpXScwh@krava>
Date: Mon, 18 Mar 2024 10:58:54 +0100
From: Jiri Olsa <olsajiri@...il.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>, Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>, 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 2/2] selftests/bpf: add selftest for
 bpf_task_get_cgroup

On Sat, Mar 16, 2024 at 10:22:41AM -0600, Jose Fernandez wrote:

SNIP

> +void test_task_get_cgroup(void)
> +{
> +	struct test_task_get_cgroup *skel;
> +	int err, fd;
> +	pid_t pid;
> +	__u64 cgroup_id, expected_cgroup_id;
> +	const struct timespec req = {
> +		.tv_sec = 1,
> +		.tv_nsec = 0,
> +	};
> +
> +	fd = test__join_cgroup(TEST_CGROUP);
> +	if (!ASSERT_OK(fd < 0, "test_join_cgroup_TEST_CGROUP"))
> +		return;
> +
> +	skel = test_task_get_cgroup__open();
> +	if (!ASSERT_OK_PTR(skel, "test_task_get_cgroup__open"))
> +		goto cleanup;
> +
> +	err = test_task_get_cgroup__load(skel);
> +	if (!ASSERT_OK(err, "test_task_get_cgroup__load"))
> +		goto cleanup;

nit, you could call test_task_get_cgroup__open_and_load

> +
> +	err = test_task_get_cgroup__attach(skel);
> +	if (!ASSERT_OK(err, "test_task_get_cgroup__attach"))
> +		goto cleanup;
> +
> +	pid = getpid();
> +	expected_cgroup_id = get_cgroup_id(TEST_CGROUP);
> +	if (!ASSERT_GT(expected_cgroup_id, 0, "get_cgroup_id"))
> +		goto cleanup;
> +
> +	/* Trigger nanosleep to enter the sched_switch tracepoint */
> +	/* The previous task should be this process */
> +	syscall(__NR_nanosleep, &req, NULL);

would smaller sleep do? also we have our own usleep (in test_progs.c)
that calls nanosleep

> +
> +	err = bpf_map_lookup_elem(bpf_map__fd(skel->maps.pid_to_cgid_map), &pid,
> +				  &cgroup_id);
> +
> +	if (!ASSERT_OK(err, "bpf_map_lookup_elem"))
> +		goto cleanup;
> +
> +	ASSERT_EQ(cgroup_id, expected_cgroup_id, "cgroup_id");
> +
> +cleanup:
> +	test_task_get_cgroup__destroy(skel);
> +	close(fd);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_task_get_cgroup.c b/tools/testing/selftests/bpf/progs/test_task_get_cgroup.c
> new file mode 100644
> index 000000000000..580f8f0657d5
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_task_get_cgroup.c
> @@ -0,0 +1,37 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright 2024 Netflix, Inc.
> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +struct cgroup *bpf_task_get_cgroup(struct task_struct *task) __ksym;
> +void bpf_cgroup_release(struct cgroup *cgrp) __ksym;
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_HASH);
> +	__uint(max_entries, 4096);
> +	__type(key, __u32);
> +	__type(value, __u64);
> +} pid_to_cgid_map SEC(".maps");
> +
> +SEC("tp_btf/sched_switch")
> +int BPF_PROG(sched_switch, bool preempt, struct task_struct *prev,
> +	     struct task_struct *next)
> +{
> +	struct cgroup *cgrp;
> +	u64 cgroup_id;
> +	u32 pid;
> +

could you filter for your pid in here like we do in other places,
(eg in progs/kprobe_multi.c)

in which case you won't need hash map, but just a single value
to store the cgroup id to

jirka

> +	cgrp = bpf_task_get_cgroup(prev);
> +	if (cgrp == NULL)
> +		return 0;
> +	cgroup_id = cgrp->kn->id;
> +	pid = prev->pid;
> +	bpf_map_update_elem(&pid_to_cgid_map, &pid, &cgroup_id, BPF_ANY);
> +
> +	bpf_cgroup_release(cgrp);
> +	return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> -- 
> 2.40.1
>