Fix test_cgroup_iter_memcg issues found during back-porting

PATCH Applied Hui Zhu 2 participants 4 messages Mar 3 – Mar 10

Subsystems (3)

Kselftest BPF BPF selftests

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Hui Zhu

author

2026-03-03 05:53 UTC #0 lore raw

v5 cover Fix test_cgroup_iter_memcg issues found during back-porting

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.
The test_cgroup_iter_memcg test would falsely pass when bpf_mem_cgroup_page_state() failed due to incompatible enum values across kernel versions. Additionally, test_kmem would fail on systems with cgroup.memory=nokmem enabled.

These patches are my fixes for the problems I encountered.

Changelog:
v5:
According to the comments of Emil Tsalapatis and JP Kobryn, dropped "selftests/bpf: Check bpf_mem_cgroup_page_state return value". v4:
Fixed wrong git commit log in "bpf: Use bpf_core_enum_value for stats in cgroup_iter_memcg".
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 (2):
selftests/bpf: Remove kmem subtest from cgroup_iter_memcg
bpf: Use bpf_core_enum_value for stats in cgroup_iter_memcg

 .../testing/selftests/bpf/cgroup_iter_memcg.h |  2 --
 .../bpf/prog_tests/cgroup_iter_memcg.c        | 28 -------------------
 .../selftests/bpf/progs/cgroup_iter_memcg.c   | 18 ++++++++----
 3 files changed, 12 insertions(+), 36 deletions(-)

Signature · 1 line

2.43.0

Hui Zhu

author

2026-03-03 05:54 UTC #1 lore raw

PATCH v5 1/2 selftests/bpf: Remove kmem subtest from cgroup_iter_memcg

From: Hui Zhu <[email protected]>

When cgroup.memory=nokmem is set in the kernel command line, kmem accounting is disabled. This causes the test_kmem subtest in cgroup_iter_memcg to fail because it expects non-zero kmem values.

Remove the kmem subtest altogether since the remaining subtests (shmem, file, pgfault) already provide sufficient coverage for the cgroup iter memcg functionality.

Reviewed-by JP Kobryn <[email protected]>

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

---
 .../testing/selftests/bpf/cgroup_iter_memcg.h |  2 --
 .../bpf/prog_tests/cgroup_iter_memcg.c        | 28 -------------------
 .../selftests/bpf/progs/cgroup_iter_memcg.c   |  1 -
 3 files changed, 31 deletions(-)

tools/testing/selftests/bpf/cgroup_iter_memcg.h +0 -2

index 3f59b127943b..ff20ec537164 100644
@@ -9,8 +9,6 @@ struct memcg_query {
 	unsigned long nr_shmem;
 	unsigned long nr_file_pages;
 	unsigned long nr_file_mapped;
-	/* some memcg_stat_item */
-	unsigned long memcg_kmem;
 	/* some vm_event_item */
 	unsigned long pgfault;
 };

tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c +0 ~~-28~~

index a5afd16705f0..88fc3e83d2b7 100644
@@ -126,32 +126,6 @@ static void test_shmem(struct bpf_link *link, struct memcg_query *memcg_query)
 	shm_unlink("/tmp_shmem");
 }
 
-#define NR_PIPES 64
-static void test_kmem(struct bpf_link *link, struct memcg_query *memcg_query)
-{
-	int fds[NR_PIPES][2], i;
-
-	/*
-	 * Increase kmem value by creating pipes which will allocate some
-	 * kernel buffers.
-	 */
-	for (i = 0; i < NR_PIPES; i++) {
-		if (!ASSERT_OK(pipe(fds[i]), "pipe"))
-			goto cleanup;
-	}
-
-	if (!ASSERT_OK(read_stats(link), "read stats"))
-		goto cleanup;
-
-	ASSERT_GT(memcg_query->memcg_kmem, 0, "kmem value");
-
-cleanup:
-	for (i = i - 1; i >= 0; i--) {
-		close(fds[i][0]);
-		close(fds[i][1]);
-	}
-}
-
 static void test_pgfault(struct bpf_link *link, struct memcg_query *memcg_query)
 {
 	void *map;

@@ -209,8 +183,6 @@ void test_cgroup_iter_memcg(void)
 		test_shmem(link, &skel->data_query->memcg_query);
 	if (test__start_subtest("cgroup_iter_memcg__file"))
 		test_file(link, &skel->data_query->memcg_query);
-	if (test__start_subtest("cgroup_iter_memcg__kmem"))
-		test_kmem(link, &skel->data_query->memcg_query);
 	if (test__start_subtest("cgroup_iter_memcg__pgfault"))
 		test_pgfault(link, &skel->data_query->memcg_query);

tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c +0 -1

index 59fb70a3cc50..12f79a44133e 100644
@@ -30,7 +30,6 @@ int cgroup_memcg_query(struct bpf_iter__cgroup *ctx)
 	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.memcg_kmem = bpf_mem_cgroup_page_state(memcg, MEMCG_KMEM);
 	memcg_query.pgfault = bpf_mem_cgroup_vm_events(memcg, PGFAULT);
 
 	bpf_put_mem_cgroup(memcg);

Signature · 1 line

2.43.0

Hui Zhu

author

2026-03-03 05:54 UTC #2 lore raw

PATCH v5 2/2 bpf: Use bpf_core_enum_value for stats in cgroup_iter_memcg

In reply to Hui Zhu

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
- vm_event_item: PGFAULT

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

Reviewed-by Emil Tsalapatis <[email protected]>

Reviewed-by JP Kobryn <[email protected]>

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);

Signature · 1 line

2.43.0

[email protected]

CI Applied

2026-03-10 19:00 UTC #3 lore raw

In reply to Hui Zhu

This series was applied to bpf/bpf-next.git (master) by Alexei Starovoitov <[email protected]>:

Hello:

This series was applied to bpf/bpf-next.git (master) by Alexei Starovoitov <[email protected]>:

Quoted 11 lines · On Tue, 3 Mar 2026 13:53:07 +0800 you wrote:

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.
The test_cgroup_iter_memcg test would falsely pass when bpf_mem_cgroup_page_state() failed due to incompatible enum values across kernel versions. Additionally, test_kmem would fail on systems with cgroup.memory=nokmem enabled.
[...]

Here is the summary with links:
- [bpf-next,v5,1/2] selftests/bpf: Remove kmem subtest from cgroup_iter_memcg

    https://git.kernel.org/bpf/bpf-next/c/a8fce027e17b
  - [bpf-next,v5,2/2] bpf: Use bpf_core_enum_value for stats in cgroup_iter_memcg
    https://git.kernel.org/bpf/bpf-next/c/da99028c2113

You are awesome, thank you!

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