Fix test_cgroup_iter_memcg issues found during back-porting

From: Hui Zhu <[email protected]>

Replace hardcoded enum values with bpf_core_enum_value() calls in cgroup_iter_memcg test to improve portability across different kernel versions.

The change adds runtime enum value resolution for:
- node_stat_item: NR_ANON_MAPPED, NR_SHMEM, NR_FILE_PAGES, NR_FILE_MAPPED
- memcg_stat_item: MEMCG_KMEM
- vm_event_item: PGFAULT

This ensures the BPF program can adapt to enum value changes between kernel versions.

Signed-off-by Hui Zhu <[email protected]>

---
 .../selftests/bpf/progs/cgroup_iter_memcg.c     | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c +12 -5

index 12f79a44133e..06a385c9d85b 100644
@@ -26,11 +26,18 @@ int cgroup_memcg_query(struct bpf_iter__cgroup *ctx)
 
 	bpf_mem_cgroup_flush_stats(memcg);
 
-	memcg_query.nr_anon_mapped = bpf_mem_cgroup_page_state(memcg, NR_ANON_MAPPED);
-	memcg_query.nr_shmem = bpf_mem_cgroup_page_state(memcg, NR_SHMEM);
-	memcg_query.nr_file_pages = bpf_mem_cgroup_page_state(memcg, NR_FILE_PAGES);
-	memcg_query.nr_file_mapped = bpf_mem_cgroup_page_state(memcg, NR_FILE_MAPPED);
-	memcg_query.pgfault = bpf_mem_cgroup_vm_events(memcg, PGFAULT);
+	memcg_query.nr_anon_mapped = bpf_mem_cgroup_page_state(
+		memcg,
+		bpf_core_enum_value(enum node_stat_item, NR_ANON_MAPPED));
+	memcg_query.nr_shmem = bpf_mem_cgroup_page_state(
+		memcg, bpf_core_enum_value(enum node_stat_item, NR_SHMEM));
+	memcg_query.nr_file_pages = bpf_mem_cgroup_page_state(
+		memcg, bpf_core_enum_value(enum node_stat_item, NR_FILE_PAGES));
+	memcg_query.nr_file_mapped = bpf_mem_cgroup_page_state(
+		memcg,
+		bpf_core_enum_value(enum node_stat_item, NR_FILE_MAPPED));
+	memcg_query.pgfault = bpf_mem_cgroup_vm_events(
+		memcg, bpf_core_enum_value(enum vm_event_item, PGFAULT));
 
 	bpf_put_mem_cgroup(memcg);
 

From: Hui Zhu <[email protected]>

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.

This patch adds explicit checks to ensure bpf_mem_cgroup_page_state() doesn't return -1 before validating the actual statistics values.

Signed-off-by Hui Zhu <[email protected]>

---
 .../selftests/bpf/prog_tests/cgroup_iter_memcg.c       | 10 ++++++++++
 1 file changed, 10 insertions(+)

tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c +10 -0

index 88fc3e83d2b7..9eadfbd3fdb9 100644
@@ -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:

@@ -144,6 +152,8 @@ 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_vm_events PGFAULT");
 	ASSERT_GT(memcg_query->pgfault, 0, "final pgfault val");
 
 cleanup:

From: Hui Zhu <[email protected]>

While back-porting "mm: bpf kfuncs to access memcg data", I encountered issues with test_cgroup_iter_memcg, specifically in test_kmem.

These patches are my fixes for the problems I encountered.

Changelog:
v3:
According to the comments of JP Kobryn, remove kmem subtest from cgroup_iter_memcg and fix assertion string in test_pgfault. v2:
According to the comments of JP Kobryn, added bpf_core_enum_value() usage in the BPF program to handle cross-kernel enum value differences at load-time instead of compile-time.
Dropped the mm/memcontrol.c patch.
Modified test_kmem handling: instead of skipping when nokmem is set, verify that kmem value is zero as expected.
According to the comments of bot, fixed assertion message: changed "bpf_mem_cgroup_page_state" to "bpf_mem_cgroup_vm_events" for PGFAULT check.

Hui Zhu (3):
selftests/bpf: Remove kmem subtest from cgroup_iter_memcg
bpf: Use bpf_core_enum_value for stats in cgroup_iter_memcg selftests/bpf: Check bpf_mem_cgroup_page_state return value

 .../testing/selftests/bpf/cgroup_iter_memcg.h |  2 -
 .../bpf/prog_tests/cgroup_iter_memcg.c        | 38 +++++--------------
 .../selftests/bpf/progs/cgroup_iter_memcg.c   | 18 ++++++---
 3 files changed, 22 insertions(+), 36 deletions(-)

Quoted 6 lines · Hui Zhu

From: Hui Zhu <[email protected]>

While back-porting "mm: bpf kfuncs to access memcg data", I encountered issues with test_cgroup_iter_memcg, specifically in test_kmem.

Quoted 2 lines

These patches are my fixes for the problems I encountered.

Nit: Could you be a bit more descriptive about the series' contents? Cover letters normally focus on what what the patch does - for example the issues being found during backporting is not pertinent to the patchset itself, because the issues are still present on bpf-next.

Quoted 24 lines

Changelog:
v3:
According to the comments of JP Kobryn, remove kmem subtest from cgroup_iter_memcg and fix assertion string in test_pgfault. v2:
According to the comments of JP Kobryn, added bpf_core_enum_value() usage in the BPF program to handle cross-kernel enum value differences at load-time instead of compile-time.
Dropped the mm/memcontrol.c patch.
Modified test_kmem handling: instead of skipping when nokmem is set, verify that kmem value is zero as expected.
According to the comments of bot, fixed assertion message: changed "bpf_mem_cgroup_page_state" to "bpf_mem_cgroup_vm_events" for PGFAULT check.

Hui Zhu (3):
selftests/bpf: Remove kmem subtest from cgroup_iter_memcg
bpf: Use bpf_core_enum_value for stats in cgroup_iter_memcg selftests/bpf: Check bpf_mem_cgroup_page_state return value

 .../testing/selftests/bpf/cgroup_iter_memcg.h |  2 -
 .../bpf/prog_tests/cgroup_iter_memcg.c        | 38 +++++--------------
 .../selftests/bpf/progs/cgroup_iter_memcg.c   | 18 ++++++---
 3 files changed, 22 insertions(+), 36 deletions(-)