lib/prime_numbers: convert self-test to KUnit

Extract a private header and convert the prime_numbers self-test to a
KUnit test. I considered parameterizing the test using
`KUNIT_CASE_PARAM` but didn't see how it was possible since the test
logic is entangled with the test parameter generation logic.

Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Link: https://lore.kernel.org/r/20250208-prime_numbers-kunit-convert-v5-2-b0cb82ae7c7d@gmail.com
Signed-off-by: Kees Cook <kees@kernel.org>

lib/Kconfig.debug

@@ -3235,6 +3235,20 @@ config GCD_KUNIT_TEST
 
 	  If unsure, say N
 
+config PRIME_NUMBERS_KUNIT_TEST
+	tristate "Prime number generator test" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	select PRIME_NUMBERS
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables the KUnit test suite for the {is,next}_prime_number
+	  functions.
+
+	  Enabling this option will include tests that compare the prime number
+	  generator functions against a brute force implementation.
+
+	  If unsure, say N
+
 endif # RUNTIME_TESTING_MENU
 
 config ARCH_USE_MEMTEST

lib/math/prime_numbers.c

@@ -1,16 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0-only
-#define pr_fmt(fmt) "prime numbers: " fmt
 
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/prime_numbers.h>
 #include <linux/slab.h>
 
-struct primes {
+#include "prime_numbers_private.h"
-	struct rcu_head rcu;
-	unsigned long last, sz;
-	unsigned long primes[];
-};
 
 #if BITS_PER_LONG == 64
 static const struct primes small_primes = {
@@ -62,9 +57,25 @@ static const struct primes small_primes = {
 static DEFINE_MUTEX(lock);
 static const struct primes __rcu *primes = RCU_INITIALIZER(&small_primes);
 
-static unsigned long selftest_max;
+#if IS_ENABLED(CONFIG_PRIME_NUMBERS_KUNIT_TEST)
+/*
+ * Calls the callback under RCU lock. The callback must not retain
+ * the primes pointer.
+ */
+void with_primes(void *ctx, primes_fn fn)
+{
+	rcu_read_lock();
+	fn(ctx, rcu_dereference(primes));
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL(with_primes);
 
-static bool slow_is_prime_number(unsigned long x)
+EXPORT_SYMBOL(slow_is_prime_number);
+
+#else
+static
+#endif
+bool slow_is_prime_number(unsigned long x)
 {
 	unsigned long y = int_sqrt(x);
 
@@ -239,77 +250,13 @@ bool is_prime_number(unsigned long x)
 }
 EXPORT_SYMBOL(is_prime_number);
 
-static void dump_primes(void)
-{
-	const struct primes *p;
-	char *buf;
-
-	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
-
-	rcu_read_lock();
-	p = rcu_dereference(primes);
-
-	if (buf)
-		bitmap_print_to_pagebuf(true, buf, p->primes, p->sz);
-	pr_info("primes.{last=%lu, .sz=%lu, .primes[]=...x%lx} = %s\n",
-		p->last, p->sz, p->primes[BITS_TO_LONGS(p->sz) - 1], buf);
-
-	rcu_read_unlock();
-
-	kfree(buf);
-}
-
-static int selftest(unsigned long max)
-{
-	unsigned long x, last;
-
-	if (!max)
-		return 0;
-
-	for (last = 0, x = 2; x < max; x++) {
-		bool slow = slow_is_prime_number(x);
-		bool fast = is_prime_number(x);
-
-		if (slow != fast) {
-			pr_err("inconsistent result for is-prime(%lu): slow=%s, fast=%s!\n",
-			       x, slow ? "yes" : "no", fast ? "yes" : "no");
-			goto err;
-		}
-
-		if (!slow)
-			continue;
-
-		if (next_prime_number(last) != x) {
-			pr_err("incorrect result for next-prime(%lu): expected %lu, got %lu\n",
-			       last, x, next_prime_number(last));
-			goto err;
-		}
-		last = x;
-	}
-
-	pr_info("%s(%lu) passed, last prime was %lu\n", __func__, x, last);
-	return 0;
-
-err:
-	dump_primes();
-	return -EINVAL;
-}
-
-static int __init primes_init(void)
-{
-	return selftest(selftest_max);
-}
-
 static void __exit primes_exit(void)
 {
 	free_primes();
 }
 
-module_init(primes_init);
 module_exit(primes_exit);
 
-module_param_named(selftest, selftest_max, ulong, 0400);
-
 MODULE_AUTHOR("Intel Corporation");
 MODULE_DESCRIPTION("Prime number library");
 MODULE_LICENSE("GPL");

lib/math/prime_numbers_private.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/types.h>
+
+struct primes {
+	struct rcu_head rcu;
+	unsigned long last, sz;
+	unsigned long primes[];
+};
+
+#if IS_ENABLED(CONFIG_PRIME_NUMBERS_KUNIT_TEST)
+typedef void (*primes_fn)(void *, const struct primes *);
+
+void with_primes(void *ctx, primes_fn fn);
+bool slow_is_prime_number(unsigned long x);
+#endif

lib/math/tests/Makefile

@@ -4,4 +4,5 @@ obj-$(CONFIG_GCD_KUNIT_TEST)		+= gcd_kunit.o
 obj-$(CONFIG_INT_LOG_KUNIT_TEST)	+= int_log_kunit.o
 obj-$(CONFIG_INT_POW_KUNIT_TEST)	+= int_pow_kunit.o
 obj-$(CONFIG_INT_SQRT_KUNIT_TEST)	+= int_sqrt_kunit.o
+obj-$(CONFIG_PRIME_NUMBERS_KUNIT_TEST)	+= prime_numbers_kunit.o
 obj-$(CONFIG_RATIONAL_KUNIT_TEST)	+= rational_kunit.o

lib/math/tests/prime_numbers_kunit.c

@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <kunit/test.h>
+#include <linux/module.h>
+#include <linux/prime_numbers.h>
+
+#include "../prime_numbers_private.h"
+
+static void dump_primes(void *ctx, const struct primes *p)
+{
+	static char buf[PAGE_SIZE];
+	struct kunit_suite *suite = ctx;
+
+	bitmap_print_to_pagebuf(true, buf, p->primes, p->sz);
+	kunit_info(suite, "primes.{last=%lu, .sz=%lu, .primes[]=...x%lx} = %s",
+		   p->last, p->sz, p->primes[BITS_TO_LONGS(p->sz) - 1], buf);
+}
+
+static void prime_numbers_test(struct kunit *test)
+{
+	const unsigned long max = 65536;
+	unsigned long x, last, next;
+
+	for (last = 0, x = 2; x < max; x++) {
+		const bool slow = slow_is_prime_number(x);
+		const bool fast = is_prime_number(x);
+
+		KUNIT_ASSERT_EQ_MSG(test, slow, fast, "is-prime(%lu)", x);
+
+		if (!slow)
+			continue;
+
+		next = next_prime_number(last);
+		KUNIT_ASSERT_EQ_MSG(test, next, x, "next-prime(%lu)", last);
+		last = next;
+	}
+}
+
+static void kunit_suite_exit(struct kunit_suite *suite)
+{
+	with_primes(suite, dump_primes);
+}
+
+static struct kunit_case prime_numbers_cases[] = {
+	KUNIT_CASE(prime_numbers_test),
+	{},
+};
+
+static struct kunit_suite prime_numbers_suite = {
+	.name = "math-prime_numbers",
+	.suite_exit = kunit_suite_exit,
+	.test_cases = prime_numbers_cases,
+};
+
+kunit_test_suite(prime_numbers_suite);
+
+MODULE_AUTHOR("Intel Corporation");
+MODULE_DESCRIPTION("Prime number library");
+MODULE_LICENSE("GPL");

tools/testing/selftests/lib/config

@@ -1,5 +1,4 @@
 CONFIG_TEST_PRINTF=m
 CONFIG_TEST_SCANF=m
 CONFIG_TEST_BITMAP=m
-CONFIG_PRIME_NUMBERS=m
 CONFIG_TEST_BITOPS=m

tools/testing/selftests/lib/prime_numbers.sh

@@ -1,4 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0
-# Checks fast/slow prime_number generation for inconsistencies
-$(dirname $0)/../kselftest/module.sh "prime numbers" prime_numbers selftest=65536