Re: [PATCH V3 bpf-next 2/2] selftests/bpf: add selftest for bpf_task_get_cgroup

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Mar 18, 2024 at 11:03:02PM -0600, Jose Fernandez wrote:
> This patch adds a selftest for the `bpf_task_get_cgroup` kfunc. The test
> focuses on the use case of obtaining the cgroup ID of the previous task
> in a `sched_switch` tracepoint.
> 
> The selftest involves creating a test cgroup, attaching a BPF program
> that utilizes the `bpf_task_get_cgroup` during a `sched_switch`
> tracepoint, and validating that the obtained cgroup ID for the previous
> task matches the expected cgroup ID.
> 
> Signed-off-by: Jose Fernandez <josef@netflix.com>
> Reviewed-by: Tycho Andersen <tycho@tycho.pizza>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
> V2 -> v3: Use _open_and_load(), usleep helper, and drop map usage
> V1 -> V2: Refactor test to work with a cgroup pointer instead of the ID
> 
>  .../bpf/prog_tests/task_get_cgroup.c          | 43 +++++++++++++++++++
>  .../bpf/progs/test_task_get_cgroup.c          | 32 ++++++++++++++
>  2 files changed, 75 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/task_get_cgroup.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_task_get_cgroup.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/task_get_cgroup.c b/tools/testing/selftests/bpf/prog_tests/task_get_cgroup.c
> new file mode 100644
> index 000000000000..031623067e7e
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/task_get_cgroup.c
> @@ -0,0 +1,43 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright 2024 Netflix, Inc.
> +
> +#include <test_progs.h>
> +#include <cgroup_helpers.h>
> +#include "test_task_get_cgroup.skel.h"
> +#include <unistd.h>
> +
> +#define TEST_CGROUP "/test-task-get-cgroup/"
> +
> +void test_task_get_cgroup(void)
> +{
> +	struct test_task_get_cgroup *skel;
> +	int err, fd;
> +	__u64 expected_cgroup_id;
> +
> +	fd = test__join_cgroup(TEST_CGROUP);
> +	if (!ASSERT_OK(fd < 0, "test_join_cgroup_TEST_CGROUP"))
> +		return;
> +
> +	skel = test_task_get_cgroup__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "test_task_get_cgroup__open_and_load"))
> +		goto cleanup;
> +
> +	err = test_task_get_cgroup__attach(skel);
> +	if (!ASSERT_OK(err, "test_task_get_cgroup__attach"))
> +		goto cleanup;
> +
> +	skel->bss->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 */
> +	usleep(100);
> +
> +	ASSERT_EQ(skel->bss->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..30d4499c6bc5
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_task_get_cgroup.c
> @@ -0,0 +1,32 @@
> +// 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;
> +
> +int pid = 0;
> +u64 cgroup_id = 0;
> +
> +SEC("tp_btf/sched_switch")
> +int BPF_PROG(sched_switch, bool preempt, struct task_struct *prev,
> +	     struct task_struct *next)
> +{
> +	struct cgroup *cgrp;
> +
> +	if (prev->pid != pid)
> +		return 0;
> +
> +	cgrp = bpf_task_get_cgroup(prev);
> +	if (cgrp == NULL)
> +		return 0;
> +	cgroup_id = cgrp->kn->id;
> +
> +	bpf_cgroup_release(cgrp);
> +	return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> -- 
> 2.40.1
>