selftests/bpf: Add tests for rqspinlock

Introduce selftests that trigger AA, ABBA deadlocks, and test the edge
case where the held locks table runs out of entries, since we then
fallback to the timeout as the final line of defense. Also exercise
verifier's AA detection where applicable.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250316040541.108729-26-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 98 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/res_spin_lock.c b/tools/testing/selftests/bpf/prog_tests/res_spin_lock.c
new file mode 100644
index 000000000000..115287ba441b
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/res_spin_lock.c
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024-2025 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include <network_helpers.h>
+#include <sys/sysinfo.h>
+
+#include "res_spin_lock.skel.h"
+#include "res_spin_lock_fail.skel.h"
+
+void test_res_spin_lock_failure(void)
+{
+	RUN_TESTS(res_spin_lock_fail);
+}
+
+static volatile int skip;
+
+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 = 10000,
+	);
+
+	while (!READ_ONCE(skip)) {
+		err = bpf_prog_test_run_opts(prog_fd, &topts);
+		ASSERT_OK(err, "test_run");
+		ASSERT_OK(topts.retval, "test_run retval");
+	}
+	pthread_exit(arg);
+}
+
+void test_res_spin_lock_success(void)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.repeat = 1,
+	);
+	struct res_spin_lock *skel;
+	pthread_t thread_id[16];
+	int prog_fd, i, err;
+	void *ret;
+
+	if (get_nprocs() < 2) {
+		test__skip();
+		return;
+	}
+
+	skel = res_spin_lock__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "res_spin_lock__open_and_load"))
+		return;
+	/* AA deadlock */
+	prog_fd = bpf_program__fd(skel->progs.res_spin_lock_test);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	ASSERT_OK(err, "error");
+	ASSERT_OK(topts.retval, "retval");
+
+	prog_fd = bpf_program__fd(skel->progs.res_spin_lock_test_held_lock_max);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	ASSERT_OK(err, "error");
+	ASSERT_OK(topts.retval, "retval");
+
+	/* Multi-threaded ABBA deadlock. */
+
+	prog_fd = bpf_program__fd(skel->progs.res_spin_lock_test_AB);
+	for (i = 0; i < 16; i++) {
+		int err;
+
+		err = pthread_create(&thread_id[i], NULL, &spin_lock_thread, &prog_fd);
+		if (!ASSERT_OK(err, "pthread_create"))
+			goto end;
+	}
+
+	topts.retval = 0;
+	topts.repeat = 1000;
+	int fd = bpf_program__fd(skel->progs.res_spin_lock_test_BA);
+	while (!topts.retval && !err && !READ_ONCE(skel->bss->err)) {
+		err = bpf_prog_test_run_opts(fd, &topts);
+	}
+
+	WRITE_ONCE(skip, true);
+
+	for (i = 0; i < 16; i++) {
+		if (!ASSERT_OK(pthread_join(thread_id[i], &ret), "pthread_join"))
+			goto end;
+		if (!ASSERT_EQ(ret, &prog_fd, "ret == prog_fd"))
+			goto end;
+	}
+
+	ASSERT_EQ(READ_ONCE(skel->bss->err), -EDEADLK, "timeout err");
+	ASSERT_OK(err, "err");
+	ASSERT_EQ(topts.retval, -EDEADLK, "timeout");
+end:
+	res_spin_lock__destroy(skel);
+	return;
+}