Re: [PATCH V2 bpf-next 2/2] selftests/bpf: add selftest for bpf_task_get_cgroup

On 2024-03-16 at 21:52:41, Jose Fernandez (josef@netflix.com) 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

---

V1 -> V2: Refactor test to work with a cgroup pointer instead of the ID

.../bpf/prog_tests/task_get_cgroup.c | 58 +++++++++++++++++++ .../bpf/progs/test_task_get_cgroup.c | 37 ++++++++++++ 2 files changed, 95 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..67ed65d0c461 --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/task_get_cgroup.c @@ -0,0 +1,58 @@ +// 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;
• pid_t pid;
• __u64 cgroup_id, expected_cgroup_id;
• const struct timespec req = {

• .tv_sec = 1,
  

• .tv_nsec = 0,
  

• };

Reverse Xmas tree.

• 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;
  

• 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);
• 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;
• 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