Merge branch 'fix-test_cgroup_iter_memcg-issues-found-during-back-porting'

Hui Zhu says:

====================
Fix test_cgroup_iter_memcg issues found during back-porting

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.
====================

Link: https://patch.msgid.link/cover.1772505399.git.zhuhui@kylinos.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Alexei Starovoitov

tools/testing/selftests/bpf/cgroup_iter_memcg.h

@@ -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

@@ -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

@@ -26,12 +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.memcg_kmem = bpf_mem_cgroup_page_state(memcg, MEMCG_KMEM);
-	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);