[RFC PATCH bpf-next 10/12] selftests/bpf: Add test for bpf_list_{front,back}

[Martin KaFai Lau <martin.lau@linux.dev>]

From: Martin KaFai Lau <martin.lau@kernel.org>

This patch adds a test for the new bpf_list_{front,back} kfunc.

It also adds a test to ensure the non-owning node pointer cannot
be used after unlock.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
 .../selftests/bpf/prog_tests/linked_list.c    |   2 +
 .../selftests/bpf/progs/linked_list_peek.c    | 104 ++++++++++++++++++
 2 files changed, 106 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/linked_list_peek.c

diff --git a/tools/testing/selftests/bpf/prog_tests/linked_list.c b/tools/testing/selftests/bpf/prog_tests/linked_list.c
index 77d07e0a4a55..559f45239a83 100644
--- a/tools/testing/selftests/bpf/prog_tests/linked_list.c
+++ b/tools/testing/selftests/bpf/prog_tests/linked_list.c
@@ -7,6 +7,7 @@
 
 #include "linked_list.skel.h"
 #include "linked_list_fail.skel.h"
+#include "linked_list_peek.skel.h"
 
 static char log_buf[1024 * 1024];
 
@@ -804,4 +805,5 @@ void test_linked_list(void)
 	test_linked_list_success(LIST_IN_LIST, false);
 	test_linked_list_success(LIST_IN_LIST, true);
 	test_linked_list_success(TEST_ALL, false);
+	RUN_TESTS(linked_list_peek);
 }
diff --git a/tools/testing/selftests/bpf/progs/linked_list_peek.c b/tools/testing/selftests/bpf/progs/linked_list_peek.c
new file mode 100644
index 000000000000..26c978091e5b
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/linked_list_peek.c
@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+#include "bpf_experimental.h"
+
+struct node_data {
+	struct bpf_list_node l;
+	int key;
+};
+
+#define private(name) SEC(".data." #name) __hidden __attribute__((aligned(8)))
+private(A) struct bpf_spin_lock glock;
+private(A) struct bpf_list_head ghead __contains(node_data, l);
+
+#define list_entry(ptr, type, member) container_of(ptr, type, member)
+#define NR_NODES 32
+
+int zero = 0;
+
+SEC("syscall")
+__failure __msg("invalid mem access 'scalar'")
+long list_peek_unlock_scalar_node(void *ctx)
+{
+	struct bpf_list_node *l_n;
+	struct node_data *n;
+
+	bpf_spin_lock(&glock);
+	l_n = bpf_list_front(&ghead);
+	bpf_spin_unlock(&glock);
+
+	if (l_n) {
+		n = list_entry(l_n, struct node_data, l);
+		if (n->key == 0)
+			return __LINE__;
+	}
+
+	return 0;
+}
+
+SEC("syscall")
+__retval(0)
+long list_peek(void *ctx)
+{
+	struct bpf_list_node *l_n;
+	struct node_data *n;
+	int i, err = 0;
+
+	bpf_spin_lock(&glock);
+	l_n = bpf_list_front(&ghead);
+	bpf_spin_unlock(&glock);
+	if (l_n)
+		return __LINE__;
+
+	bpf_spin_lock(&glock);
+	l_n = bpf_list_back(&ghead);
+	bpf_spin_unlock(&glock);
+	if (l_n)
+		return __LINE__;
+
+	for (i = zero; i < NR_NODES && can_loop; i++) {
+		n = bpf_obj_new(typeof(*n));
+		if (!n)
+			return __LINE__;
+		n->key = i;
+		bpf_spin_lock(&glock);
+		bpf_list_push_back(&ghead, &n->l);
+		bpf_spin_unlock(&glock);
+	}
+
+	bpf_spin_lock(&glock);
+
+	l_n = bpf_list_front(&ghead);
+	if (!l_n) {
+		err = __LINE__;
+		goto done;
+	}
+
+	n = list_entry(l_n, struct node_data, l);
+	if (n->key != 0) {
+		err = __LINE__;
+		goto done;
+	}
+
+	l_n = bpf_list_back(&ghead);
+	if (!l_n) {
+		err = __LINE__;
+		goto done;
+	}
+
+	n = list_entry(l_n, struct node_data, l);
+	if (n->key != NR_NODES - 1) {
+		err = __LINE__;
+		goto done;
+	}
+
+done:
+	bpf_spin_unlock(&glock);
+	return err;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.47.1