diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c b/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
index 5d0a8bb110a4..e01fac401ec5 100644
--- a/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
@@ -155,28 +155,30 @@ static void reclaimer(const char *cgroup_path, size_t size)
 	int err;
 
 	/* Join cgroup in the parent process workdir */
-	join_parent_cgroup(cgroup_path);
+	if (join_parent_cgroup(cgroup_path))
+		exit(EACCES);
 
 	/* Allocate memory */
 	buf = malloc(size);
+	if(!buf)
+		exit(ENOMEM);
+
+	/* Write to memory to make sure it's actually allocated */
 	for (ptr = buf; ptr < buf + size; ptr += PAGE_SIZE)
 		*ptr = 1;
 
-	/*
-	 * Try to reclaim memory.
-	 * memory.reclaim can return EAGAIN if the amount is not
-	 * fully reclaimed.
-	 */
+	/* Try to reclaim memory */
 	snprintf(size_buf, 128, "%lu", size);
 	err = write_cgroup_file_parent(cgroup_path, "memory.reclaim", size_buf);
 
 	free(buf);
-	exit(err && errno != EAGAIN);
+	/* memory.reclaim returns EAGAIN if the amount is not fully reclaimed */
+	exit(err && errno != EAGAIN ? errno : 0);
 }
 
 static int induce_vmscan(void)
 {
-	int i, status, err = 0;
+	int i, status;
 
 	/*
 	 * In every leaf cgroup, run a child process that allocates some memory
@@ -189,13 +191,13 @@ static int induce_vmscan(void)
 		pid = fork();
 		if (pid == 0)
 			reclaimer(cgroups[i].path, MB(5));
-		if (!ASSERT_GT(pid, 0, "fork reclaimer child"))
+		if (!ASSERT_GT(pid, 0, "fork reclaimer"))
 			return pid;
 
 		/* Cleanup reclaimer child */
 		waitpid(pid, &status, 0);
-		err = !WIFEXITED(status) || WEXITSTATUS(status);
-		ASSERT_OK(err, "reclaimer child exit status");
+		ASSERT_TRUE(WIFEXITED(status), "reclaimer exited");
+		ASSERT_EQ(WEXITSTATUS(status), 0, "reclaim exit code");
 	}
 	return 0;
 }
@@ -203,7 +205,7 @@ static int induce_vmscan(void)
 static unsigned long long get_cgroup_vmscan_delay(unsigned long long cgroup_id,
 						  const char *file_name)
 {
-	char buf[128], path[128];
+	static char buf[128], path[128];
 	unsigned long long vmscan = 0, id = 0;
 	int err;
 
diff --git a/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c b/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c
index 0a1a3bebdf4c..85a65a72482e 100644
--- a/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c
+++ b/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c
@@ -37,14 +37,14 @@ struct vmscan {
 
 struct {
 	__uint(type, BPF_MAP_TYPE_PERCPU_HASH);
-	__uint(max_entries, 10);
+	__uint(max_entries, 100);
 	__type(key, __u64);
 	__type(value, struct vmscan_percpu);
 } pcpu_cgroup_vmscan_elapsed SEC(".maps");
 
 struct {
 	__uint(type, BPF_MAP_TYPE_HASH);
-	__uint(max_entries, 10);
+	__uint(max_entries, 100);
 	__type(key, __u64);
 	__type(value, struct vmscan);
 } cgroup_vmscan_elapsed SEC(".maps");
@@ -65,11 +65,13 @@ static inline uint64_t cgroup_id(struct cgroup *cgrp)
 static inline int create_vmscan_percpu_elem(__u64 cg_id, __u64 state)
 {
 	struct vmscan_percpu pcpu_init = {.state = state, .prev = 0};
+	int err;
 
-	if (bpf_map_update_elem(&pcpu_cgroup_vmscan_elapsed, &cg_id,
-				&pcpu_init, BPF_NOEXIST)) {
-		bpf_printk("failed to create pcpu entry for cgroup %llu\n"
-			   , cg_id);
+	err = bpf_map_update_elem(&pcpu_cgroup_vmscan_elapsed, &cg_id,
+				  &pcpu_init, BPF_NOEXIST);
+	if (err) {
+		bpf_printk("failed to create pcpu entry for cgroup %llu: %d\n"
+			   , cg_id, err);
 		return 1;
 	}
 	return 0;
@@ -78,11 +80,13 @@ static inline int create_vmscan_percpu_elem(__u64 cg_id, __u64 state)
 static inline int create_vmscan_elem(__u64 cg_id, __u64 state, __u64 pending)
 {
 	struct vmscan init = {.state = state, .pending = pending};
+	int err;
 
-	if (bpf_map_update_elem(&cgroup_vmscan_elapsed, &cg_id,
-				&init, BPF_NOEXIST)) {
-		bpf_printk("failed to create entry for cgroup %llu\n"
-			   , cg_id);
+	err = bpf_map_update_elem(&cgroup_vmscan_elapsed, &cg_id,
+				  &init, BPF_NOEXIST);
+	if (err) {
+		bpf_printk("failed to create entry for cgroup %llu: %d\n"
+			   , cg_id, err);
 		return 1;
 	}
 	return 0;
@@ -220,7 +224,7 @@ int BPF_PROG(dump_vmscan, struct bpf_iter_meta *meta, struct cgroup *cgrp)
 	total_stat = bpf_map_lookup_elem(&cgroup_vmscan_elapsed, &cg_id);
 	if (!total_stat) {
 		bpf_printk("error finding stats for cgroup %llu\n", cg_id);
-		BPF_SEQ_PRINTF(seq, "cg_id: %llu, total_vmscan_delay: -1\n",
+		BPF_SEQ_PRINTF(seq, "cg_id: %llu, total_vmscan_delay: 0\n",
 			       cg_id);
 		return 1;
 	}