[PATCH bpf-next 1/3] selftests/bpf: Check bpf_mem_cgroup_page_state return value

[Hui Zhu <hui.zhu@linux.dev>]

From: Hui Zhu <zhuhui@kylinos.cn>

When back-porting test_progs to different kernel versions, I encountered
an issue where the test_cgroup_iter_memcg test would falsely pass even
when bpf_mem_cgroup_page_state() failed.

The problem occurs when test_progs compiled on one kernel version is
executed on another kernel with different enum values for memory
statistics (e.g., NR_ANON_MAPPED, NR_FILE_PAGES). In such cases,
bpf_mem_cgroup_page_state() returns -1 to indicate failure, but the test
didn't check for this error condition and incorrectly reported success.

This patch adds explicit checks to ensure bpf_mem_cgroup_page_state()
doesn't return -1 before validating the actual statistics values. This
prevents false positives when running test_progs in cross-kernel
environments.

Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 .../selftests/bpf/prog_tests/cgroup_iter_memcg.c     | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c b/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
index a5afd16705f0..13b299512429 100644
--- a/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
@@ -53,6 +53,8 @@ static void test_anon(struct bpf_link *link, struct memcg_query *memcg_query)
 	if (!ASSERT_OK(read_stats(link), "read stats"))
 		goto cleanup;
 
+	ASSERT_NEQ(memcg_query->nr_anon_mapped, (unsigned long)-1,
+		  "bpf_mem_cgroup_page_state NR_ANON_MAPPED");
 	ASSERT_GT(memcg_query->nr_anon_mapped, 0, "final anon mapped val");
 
 cleanup:
@@ -88,6 +90,10 @@ static void test_file(struct bpf_link *link, struct memcg_query *memcg_query)
 	if (!ASSERT_OK(read_stats(link), "read stats"))
 		goto cleanup_map;
 
+	ASSERT_NEQ(memcg_query->nr_file_pages, (unsigned long)-1,
+		  "bpf_mem_cgroup_page_state NR_FILE_PAGES");
+	ASSERT_NEQ(memcg_query->nr_file_mapped, (unsigned long)-1,
+		  "bpf_mem_cgroup_page_state NR_FILE_MAPPED");
 	ASSERT_GT(memcg_query->nr_file_pages, 0, "final file value");
 	ASSERT_GT(memcg_query->nr_file_mapped, 0, "final file mapped value");
 
@@ -119,6 +125,8 @@ static void test_shmem(struct bpf_link *link, struct memcg_query *memcg_query)
 	if (!ASSERT_OK(read_stats(link), "read stats"))
 		goto cleanup;
 
+	ASSERT_NEQ(memcg_query->nr_shmem, (unsigned long)-1,
+		  "bpf_mem_cgroup_page_state NR_SHMEM");
 	ASSERT_GT(memcg_query->nr_shmem, 0, "final shmem value");
 
 cleanup:
@@ -143,6 +151,8 @@ static void test_kmem(struct bpf_link *link, struct memcg_query *memcg_query)
 	if (!ASSERT_OK(read_stats(link), "read stats"))
 		goto cleanup;
 
+	ASSERT_NEQ(memcg_query->memcg_kmem, (unsigned long)-1,
+		  "bpf_mem_cgroup_page_state MEMCG_KMEM");
 	ASSERT_GT(memcg_query->memcg_kmem, 0, "kmem value");
 
 cleanup:
@@ -170,6 +180,8 @@ static void test_pgfault(struct bpf_link *link, struct memcg_query *memcg_query)
 	if (!ASSERT_OK(read_stats(link), "read stats"))
 		goto cleanup;
 
+	ASSERT_NEQ(memcg_query->pgfault, (unsigned long)-1,
+		  "bpf_mem_cgroup_page_state PGFAULT");
 	ASSERT_GT(memcg_query->pgfault, 0, "final pgfault val");
 
 cleanup:
-- 
2.43.0