[RFC PATCH bpf-next 4/4] selftests/bpf: Add tests for open-coded task and css iter

[Chuyi Zhou]

This patch adds three tests to demonstrate these patterns and validating
correctness.

test1: We use bpf_for_each(process, task) to iterate all processed in the
system and search for the current process with a given pid.

test2: We create a cgroup and add the current process to the cgroup. In the
BPF program, we would use bpf_for_each(css_task, task, css) to iterate all
tasks under the cgroup. As expected, we would find the current process.

test3: We create a cgroup tree. In the BPF program, we use
bpf_for_each(css, pos, root) to iterate all descendant under the root with
post order. As expected, we would find all descendant and the last
iterating cgroup is root cgroup.

Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
---
 .../testing/selftests/bpf/prog_tests/iters.c  | 123 ++++++++++++++++++
 .../testing/selftests/bpf/progs/iters_task.c  |  83 ++++++++++++
 2 files changed, 206 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/iters_task.c

diff --git a/tools/testing/selftests/bpf/prog_tests/iters.c b/tools/testing/selftests/bpf/prog_tests/iters.c
index 10804ae5ae97..88fb565a3e97 100644
--- a/tools/testing/selftests/bpf/prog_tests/iters.c
+++ b/tools/testing/selftests/bpf/prog_tests/iters.c
@@ -2,12 +2,14 @@
 /* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
 
 #include <test_progs.h>
+#include "cgroup_helpers.h"
 
 #include "iters.skel.h"
 #include "iters_state_safety.skel.h"
 #include "iters_looping.skel.h"
 #include "iters_num.skel.h"
 #include "iters_testmod_seq.skel.h"
+#include "iters_task.skel.h"
 
 static void subtest_num_iters(void)
 {
@@ -90,6 +92,121 @@ static void subtest_testmod_seq_iters(void)
 	iters_testmod_seq__destroy(skel);
 }
 
+static void subtest_process_iters(void)
+{
+	struct iters_task *skel;
+	int err;
+
+	skel = iters_task__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		goto cleanup;
+	bpf_program__set_autoload(skel->progs.iter_task_for_each, true);
+	err = iters_task__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto cleanup;
+	skel->bss->target_pid = getpid();
+	err = iters_task__attach(skel);
+	if (!ASSERT_OK(err, "iters_task__attach"))
+		goto cleanup;
+
+	iters_task__detach(skel);
+	ASSERT_EQ(skel->bss->process_cnt, 1, "process_cnt");
+
+cleanup:
+	iters_task__destroy(skel);
+}
+
+static void subtest_css_task_iters(void)
+{
+	struct iters_task *skel;
+	int err, cg_fd, cg_id;
+	const char *cgrp_path = "/cg1";
+
+	err = setup_cgroup_environment();
+	if (!ASSERT_OK(err, "setup_cgroup_environment"))
+		goto cleanup;
+	cg_fd = create_and_get_cgroup(cgrp_path);
+	if (!ASSERT_GE(cg_fd, 0, "cg_create"))
+		goto cleanup;
+	cg_id = get_cgroup_id(cgrp_path);
+	err = join_cgroup(cgrp_path);
+	if (!ASSERT_OK(err, "setup_cgroup_environment"))
+		goto cleanup;
+
+	skel = iters_task__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		goto cleanup;
+
+	bpf_program__set_autoload(skel->progs.iter_css_task_for_each, true);
+	err = iters_task__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto cleanup;
+
+	skel->bss->target_pid = getpid();
+	skel->bss->cg_id = cg_id;
+	err = iters_task__attach(skel);
+
+	if (!ASSERT_OK(err, "iters_task__attach"))
+		goto cleanup;
+
+	iters_task__detach(skel);
+	ASSERT_EQ(skel->bss->css_task_cnt, 1, "css_task_cnt");
+
+cleanup:
+	cleanup_cgroup_environment();
+	iters_task__destroy(skel);
+}
+
+static void subtest_css_dec_iters(void)
+{
+	struct iters_task *skel;
+	struct {
+		const char *path;
+		int fd;
+	} cgs[] = {
+		{ "/cg1" },
+		{ "/cg1/cg2" },
+		{ "/cg1/cg2/cg3" },
+		{ "/cg1/cg2/cg3/cg4" },
+	};
+	int err, cg_nr = ARRAY_SIZE(cgs);
+	int i;
+
+	err = setup_cgroup_environment();
+	if (!ASSERT_OK(err, "setup_cgroup_environment"))
+		goto cleanup;
+	for (i = 0; i < cg_nr; i++) {
+		cgs[i].fd = create_and_get_cgroup(cgs[i].path);
+		if (!ASSERT_GE(cgs[i].fd, 0, "cg_create"))
+			goto cleanup;
+	}
+
+	skel = iters_task__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		goto cleanup;
+	bpf_program__set_autoload(skel->progs.iter_css_dec_for_each, true);
+	err = iters_task__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto cleanup;
+
+	skel->bss->target_pid = getpid();
+	skel->bss->cg_id = get_cgroup_id(cgs[0].path);
+
+	err = iters_task__attach(skel);
+
+	if (!ASSERT_OK(err, "iters_task__attach"))
+		goto cleanup;
+
+	iters_task__detach(skel);
+	ASSERT_EQ(skel->bss->css_dec_cnt, cg_nr, "post order search dec count");
+	ASSERT_EQ(skel->bss->last_cg_id, get_cgroup_id(cgs[0].path),
+				"post order search last cgroup id");
+
+cleanup:
+	cleanup_cgroup_environment();
+	iters_task__destroy(skel);
+}
+
 void test_iters(void)
 {
 	RUN_TESTS(iters_state_safety);
@@ -103,4 +220,10 @@ void test_iters(void)
 		subtest_num_iters();
 	if (test__start_subtest("testmod_seq"))
 		subtest_testmod_seq_iters();
+	if (test__start_subtest("process"))
+		subtest_process_iters();
+	if (test__start_subtest("css_task"))
+		subtest_css_task_iters();
+	if (test__start_subtest("css_dec"))
+		subtest_css_dec_iters();
 }
diff --git a/tools/testing/selftests/bpf/progs/iters_task.c b/tools/testing/selftests/bpf/progs/iters_task.c
new file mode 100644
index 000000000000..524926b505b0
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/iters_task.c
@@ -0,0 +1,83 @@
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+pid_t target_pid = 0;
+int process_cnt = 0;
+int css_task_cnt = 0;
+int css_dec_cnt = 0;
+
+u64 cg_id;
+u64 last_cg_id;
+
+struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
+struct cgroup *bpf_cgroup_acquire(struct cgroup *cgrp) __ksym;
+void bpf_cgroup_release(struct cgroup *p) __ksym;
+
+SEC("?tp_btf/sys_enter")
+int BPF_PROG(iter_task_for_each)
+{
+	struct task_struct *task;
+	struct task_struct *cur_task = bpf_get_current_task_btf();
+
+	if (cur_task->pid != target_pid)
+		return 0;
+
+	bpf_for_each(process, task)
+		if (task->pid == target_pid)
+			process_cnt += 1;
+
+	return 0;
+}
+
+SEC("?tp_btf/sys_enter")
+int iter_css_task_for_each(const void *ctx)
+{
+	struct task_struct *task;
+	struct task_struct *cur_task = bpf_get_current_task_btf();
+
+	if (cur_task->pid != target_pid)
+		return 0;
+
+	struct cgroup *cgrp = bpf_cgroup_from_id(cg_id);
+
+	if (cgrp == NULL)
+		return 0;
+	struct cgroup_subsys_state *css = &cgrp->self;
+
+	bpf_for_each(css_task, task, css, 0)
+		if (task->pid == target_pid)
+			css_task_cnt += 1;
+
+	bpf_cgroup_release(cgrp);
+	return 0;
+}
+
+SEC("?tp_btf/sys_enter")
+int iter_css_dec_for_each(const void *ctx)
+{
+	struct task_struct *cur_task = bpf_get_current_task_btf();
+	bool is_post_order = true;
+
+	if (cur_task->pid != target_pid)
+		return 0;
+
+	struct cgroup *cgrp = bpf_cgroup_from_id(cg_id);
+
+	if (cgrp == NULL)
+		return 0;
+	struct cgroup_subsys_state *root = &cgrp->self;
+	struct cgroup_subsys_state *pos = NULL;
+
+	bpf_for_each(css, pos, root, is_post_order) {
+		struct cgroup *cur_cgrp = pos->cgroup;
+
+		css_dec_cnt += 1;
+		if (cur_cgrp)
+			last_cg_id = cur_cgrp->kn->id;
+	}
+	bpf_cgroup_release(cgrp);
+	return 0;
+}
-- 
2.20.1