selftests/bpf: Add tests for arena spin lock

Add some basic selftests for qspinlock built over BPF arena using
cond_break_label macro.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250306035431.2186189-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/arena_spin_lock.c

@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include <network_helpers.h>
+#include <sys/sysinfo.h>
+
+struct qspinlock { int val; };
+typedef struct qspinlock arena_spinlock_t;
+
+struct arena_qnode {
+	unsigned long next;
+	int count;
+	int locked;
+};
+
+#include "arena_spin_lock.skel.h"
+
+static long cpu;
+static int repeat;
+
+pthread_barrier_t barrier;
+
+static void *spin_lock_thread(void *arg)
+{
+	int err, prog_fd = *(u32 *)arg;
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.repeat = repeat,
+	);
+	cpu_set_t cpuset;
+
+	CPU_ZERO(&cpuset);
+	CPU_SET(__sync_fetch_and_add(&cpu, 1), &cpuset);
+	ASSERT_OK(pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset), "cpu affinity");
+
+	err = pthread_barrier_wait(&barrier);
+	if (err != PTHREAD_BARRIER_SERIAL_THREAD && err != 0)
+		ASSERT_FALSE(true, "pthread_barrier");
+
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	ASSERT_OK(err, "test_run err");
+	ASSERT_EQ((int)topts.retval, 0, "test_run retval");
+
+	pthread_exit(arg);
+}
+
+static void test_arena_spin_lock_size(int size)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+	struct arena_spin_lock *skel;
+	pthread_t thread_id[16];
+	int prog_fd, i, err;
+	void *ret;
+
+	if (get_nprocs() < 2) {
+		test__skip();
+		return;
+	}
+
+	skel = arena_spin_lock__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "arena_spin_lock__open_and_load"))
+		return;
+	if (skel->data->test_skip == 2) {
+		test__skip();
+		goto end;
+	}
+	skel->bss->cs_count = size;
+	skel->bss->limit = repeat * 16;
+
+	ASSERT_OK(pthread_barrier_init(&barrier, NULL, 16), "barrier init");
+
+	prog_fd = bpf_program__fd(skel->progs.prog);
+	for (i = 0; i < 16; i++) {
+		err = pthread_create(&thread_id[i], NULL, &spin_lock_thread, &prog_fd);
+		if (!ASSERT_OK(err, "pthread_create"))
+			goto end_barrier;
+	}
+
+	for (i = 0; i < 16; i++) {
+		if (!ASSERT_OK(pthread_join(thread_id[i], &ret), "pthread_join"))
+			goto end_barrier;
+		if (!ASSERT_EQ(ret, &prog_fd, "ret == prog_fd"))
+			goto end_barrier;
+	}
+
+	ASSERT_EQ(skel->bss->counter, repeat * 16, "check counter value");
+
+end_barrier:
+	pthread_barrier_destroy(&barrier);
+end:
+	arena_spin_lock__destroy(skel);
+	return;
+}
+
+void test_arena_spin_lock(void)
+{
+	repeat = 1000;
+	if (test__start_subtest("arena_spin_lock_1"))
+		test_arena_spin_lock_size(1);
+	cpu = 0;
+	if (test__start_subtest("arena_spin_lock_1000"))
+		test_arena_spin_lock_size(1000);
+	cpu = 0;
+	repeat = 100;
+	if (test__start_subtest("arena_spin_lock_50000"))
+		test_arena_spin_lock_size(50000);
+}

tools/testing/selftests/bpf/progs/arena_spin_lock.c

@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+#include "bpf_arena_spin_lock.h"
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARENA);
+	__uint(map_flags, BPF_F_MMAPABLE);
+	__uint(max_entries, 100); /* number of pages */
+#ifdef __TARGET_ARCH_arm64
+	__ulong(map_extra, 0x1ull << 32); /* start of mmap() region */
+#else
+	__ulong(map_extra, 0x1ull << 44); /* start of mmap() region */
+#endif
+} arena SEC(".maps");
+
+int cs_count;
+
+#if defined(ENABLE_ATOMICS_TESTS) && defined(__BPF_FEATURE_ADDR_SPACE_CAST)
+arena_spinlock_t __arena lock;
+int test_skip = 1;
+#else
+int test_skip = 2;
+#endif
+
+int counter;
+int limit;
+
+SEC("tc")
+int prog(void *ctx)
+{
+	int ret = -2;
+
+#if defined(ENABLE_ATOMICS_TESTS) && defined(__BPF_FEATURE_ADDR_SPACE_CAST)
+	unsigned long flags;
+
+	if ((ret = arena_spin_lock_irqsave(&lock, flags)))
+		return ret;
+	if (counter != limit)
+		counter++;
+	bpf_repeat(cs_count);
+	ret = 0;
+	arena_spin_unlock_irqrestore(&lock, flags);
+#endif
+	return ret;
+}
+
+char _license[] SEC("license") = "GPL";