[PATCH bpf 2/2] selftests/bpf: Test per-cpu initialization of a BPF_F_CPU created element

[Donggeun Yoo]

The existing cpu_flag subtests always prime a key with BPF_F_ALL_CPUS
before any BPF_F_CPU write, so the element always exists by the time the
flag is used and the create path is never covered.

Add a subtest that creates the element with BPF_F_CPU on a map whose
max_entries is 1, so the key can only reuse the element the previous key
released, and check that the CPUs the update did not name read back zero
rather than the previous key's value.  Run it for PERCPU_HASH both
preallocated and BPF_F_NO_PREALLOC, whose per-cpu areas are recycled by
different allocators, and for LRU_PERCPU_HASH, which is always
preallocated.

Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@xxxxxxxxx>
---
 .../selftests/bpf/prog_tests/percpu_alloc.c   | 74 +++++++++++++++++++
 1 file changed, 74 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/percpu_alloc.c b/tools/testing/selftests/bpf/prog_tests/percpu_alloc.c
index a72ae0b29f6e9..d0084a2405bed 100644
--- a/tools/testing/selftests/bpf/prog_tests/percpu_alloc.c
+++ b/tools/testing/selftests/bpf/prog_tests/percpu_alloc.c
@@ -350,6 +350,74 @@ static void test_lru_percpu_hash_cpu_flag(void)
 	test_percpu_map_cpu_flag(BPF_MAP_TYPE_LRU_PERCPU_HASH);
 }
 
+/* A BPF_F_CPU update that creates an element must zero the value on the other
+ * cpus, rather than leave them holding whatever the recycled element last
+ * contained.  max_entries is 1 so the second key can only reuse the element
+ * the first one released.
+ */
+static void test_percpu_map_cpu_flag_create(enum bpf_map_type map_type, __u32 map_flags)
+{
+	LIBBPF_OPTS(bpf_map_create_opts, opts, .map_flags = map_flags);
+	const u32 stale = 0xDEADC0DE, fresh = 0xC0FFEE;
+	int nr_cpus, cpu, map_fd, err, key;
+	u32 value;
+	u64 flags;
+
+	nr_cpus = libbpf_num_possible_cpus();
+	if (!ASSERT_GT(nr_cpus, 1, "libbpf_num_possible_cpus"))
+		return;
+
+	map_fd = bpf_map_create(map_type, "cpu_flag_create", sizeof(key), sizeof(value), 1, &opts);
+	if (!ASSERT_GE(map_fd, 0, "bpf_map_create"))
+		return;
+
+	key = 1;
+	value = stale;
+	err = bpf_map_update_elem(map_fd, &key, &value, BPF_F_ALL_CPUS);
+	if (!ASSERT_OK(err, "bpf_map_update_elem all_cpus"))
+		goto out;
+
+	err = bpf_map_delete_elem(map_fd, &key);
+	if (!ASSERT_OK(err, "bpf_map_delete_elem"))
+		goto out;
+
+	key = 2;
+	value = fresh;
+	flags = BPF_F_CPU;
+	err = bpf_map_update_elem(map_fd, &key, &value, flags);
+	if (!ASSERT_OK(err, "bpf_map_update_elem specified cpu"))
+		goto out;
+
+	for (cpu = 0; cpu < nr_cpus; cpu++) {
+		value = 0;
+		flags = (u64)cpu << 32 | BPF_F_CPU;
+		err = bpf_map_lookup_elem_flags(map_fd, &key, &value, flags);
+		if (!ASSERT_OK(err, "bpf_map_lookup_elem_flags specified cpu"))
+			goto out;
+		if (!ASSERT_EQ(value, cpu ? 0 : fresh, "value on specified cpu"))
+			goto out;
+	}
+
+out:
+	close(map_fd);
+}
+
+static void test_percpu_hash_cpu_flag_create(void)
+{
+	test_percpu_map_cpu_flag_create(BPF_MAP_TYPE_PERCPU_HASH, 0);
+}
+
+static void test_percpu_hash_cpu_flag_create_malloc(void)
+{
+	test_percpu_map_cpu_flag_create(BPF_MAP_TYPE_PERCPU_HASH, BPF_F_NO_PREALLOC);
+}
+
+static void test_lru_percpu_hash_cpu_flag_create(void)
+{
+	/* lru without prealloc is -ENOTSUPP, so there is no malloc variant. */
+	test_percpu_map_cpu_flag_create(BPF_MAP_TYPE_LRU_PERCPU_HASH, 0);
+}
+
 static void test_percpu_cgroup_storage_cpu_flag(void)
 {
 	struct percpu_alloc_array *skel = NULL;
@@ -454,6 +522,12 @@ void test_percpu_alloc(void)
 		test_percpu_hash_cpu_flag();
 	if (test__start_subtest("cpu_flag_lru_percpu_hash"))
 		test_lru_percpu_hash_cpu_flag();
+	if (test__start_subtest("cpu_flag_create_percpu_hash"))
+		test_percpu_hash_cpu_flag_create();
+	if (test__start_subtest("cpu_flag_create_percpu_hash_malloc"))
+		test_percpu_hash_cpu_flag_create_malloc();
+	if (test__start_subtest("cpu_flag_create_lru_percpu_hash"))
+		test_lru_percpu_hash_cpu_flag_create();
 	if (test__start_subtest("cpu_flag_percpu_cgroup_storage"))
 		test_percpu_cgroup_storage_cpu_flag();
 	if (test__start_subtest("cpu_flag_array"))
-- 
2.53.0