selftests/bpf: libarena: Add parallel bitmap selftest

Add a selftest for testing the atomic bitmap set/clear/
test_and_set/test_and_clear operations. The selftest
checks atomicity by spawning two threads, each of which
either only works on even bits or with odd bits. The
test checks that threads do not affect each other's
bits.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/bpf/20260706181730.21731-7-emil@etsalapatis.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

tools/testing/selftests/bpf/libarena/selftests/test_parallel_bitmap.bpf.c

@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
+
+#include <bpf_atomic.h>
+
+#include <libarena/common.h>
+
+#include <libarena/asan.h>
+#include <libarena/bitmap.h>
+
+#define TEST_BITMAP_THREADS	2
+#define TEST_BITMAP_BITS	(2 * BITS_PER_LONG_LONG)
+#define TEST_BITMAP_SYNC_SPINS	BPF_MAX_LOOPS
+#define TEST_BITMAP_ITERS	10 * 1000 * 1000
+
+static struct bitmap __arena *bitmap;
+static volatile u64 started;
+static volatile bool test_abort;
+
+/*
+ * The test needs cmpxchg atomics on arena memory.
+ */
+#if defined(ENABLE_ATOMICS_TESTS) &&				  \
+	(defined(__TARGET_ARCH_arm64) || defined(__TARGET_ARCH_x86) || \
+	 defined(__TARGET_ARCH_s390) || \
+	 defined(__TARGET_ARCH_powerpc) ||				  \
+	 (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64))
+static bool bitmap_tests_enabled(void)
+{
+	return true;
+}
+#else
+static bool bitmap_tests_enabled(void)
+{
+	return false;
+}
+#endif
+
+__weak
+int bitmap_wait_for_start(void)
+{
+	u64 i;
+
+	__sync_fetch_and_add(&started, 1);
+
+	for (i = zero; i < TEST_BITMAP_SYNC_SPINS && can_loop; i++) {
+		if (test_abort)
+			return -EINTR;
+		if (smp_load_acquire(&started) >= TEST_BITMAP_THREADS)
+			return 0;
+	}
+
+	test_abort = true;
+	return -ETIMEDOUT;
+}
+
+/*
+ * The test makes sure writes don't clobber each other by overwriting
+ * the same word. One thread always writes on even bits, the other on
+ * odds. Both should be able to operate on the bitmap oblivious of the
+ * other's operations.
+ */
+__weak
+int bitmap_test_bit_sequence(u32 bit)
+{
+	if (bmp_test_and_clear_bit(bit, bitmap))
+		return -EINVAL;
+
+	if (bmp_test_and_set_bit(bit, bitmap))
+		return -EINVAL;
+	if (!bmp_test_bit(bit, bitmap))
+		return -EINVAL;
+
+	if (!bmp_test_and_set_bit(bit, bitmap))
+		return -EINVAL;
+	if (!bmp_test_bit(bit, bitmap))
+		return -EINVAL;
+
+	if (!bmp_test_and_clear_bit(bit, bitmap))
+		return -EINVAL;
+	if (bmp_test_bit(bit, bitmap))
+		return -EINVAL;
+
+	if (bmp_test_and_clear_bit(bit, bitmap))
+		return -EINVAL;
+
+	bmp_set_bit(bit, bitmap);
+	if (!bmp_test_bit(bit, bitmap))
+		return -EINVAL;
+
+	bmp_clear_bit(bit, bitmap);
+	if (bmp_test_bit(bit, bitmap))
+		return -EINVAL;
+
+	bmp_set_bit(bit, bitmap);
+	if (!bmp_test_bit(bit, bitmap))
+		return -EINVAL;
+
+	return 0;
+
+}
+
+static void bitmap_test_reset_single(int parity)
+{
+	u32 bit;
+
+	for (bit = parity; bit < TEST_BITMAP_BITS && can_loop; bit += 2)
+		bmp_clear_bit(bit, bitmap);
+
+}
+
+static int bitmap_test_common_single(int parity)
+{
+	u32 bit;
+	int ret;
+
+	for (bit = parity; bit < TEST_BITMAP_BITS && can_loop; bit += 2) {
+		if (test_abort)
+			return -EINTR;
+
+		ret = bitmap_test_bit_sequence(bit);
+		if (ret) {
+			test_abort = true;
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static int bitmap_test_common(int parity)
+{
+	int ret;
+	u32 i;
+
+	arena_subprog_init();
+
+	ret = bitmap_wait_for_start();
+	if (ret)
+		return ret;
+
+	for (i = zero; i < TEST_BITMAP_ITERS && can_loop; i++) {
+		ret = bitmap_test_common_single(parity);
+		if (ret)
+			return ret;
+
+		if (test_abort)
+			break;
+
+		bitmap_test_reset_single(parity);
+	}
+
+	return 0;
+}
+
+SEC("syscall") int parallel_test_bitmap__enabled(void)
+{
+	return bitmap_tests_enabled() ? 0 : -EOPNOTSUPP;
+}
+
+SEC("syscall") int parallel_test_bitmap__init(void)
+{
+	bitmap = bmp_alloc(TEST_BITMAP_BITS);
+	if (!bitmap)
+		return -ENOMEM;
+
+	return 0;
+}
+
+SEC("syscall") int parallel_test_bitmap__fini(void)
+{
+	int ret = 0;
+
+	if (!bitmap)
+		return -EINVAL;
+
+	bmp_free(bitmap);
+	bitmap = NULL;
+
+	return ret;
+}
+
+SEC("syscall") int parallel_test_bitmap__0(void)
+{
+	return bitmap_test_common(0);
+}
+
+SEC("syscall") int parallel_test_bitmap__1(void)
+{
+	return bitmap_test_common(1);
+}