thunderbolt: Fix NULL dereference in tb_remove_work()grafted

There is a slight race between tb_remove_work() and tb_domain_remove()
which leads to dereferencing a NULL tb->root_switch pointer inside
tb_free_unplugged_xdomains():

        Thread A                            Thread B

  tb_remove_work()
                                    tb_domain_remove()
                                      mutex_lock(&tb->lock)
                                      tb_stop()
                                        /* doesn't cancel a running callback */
                                        cancel_delayed_work(&tcm->remove_work)
                                        ...
                                        tb_switch_remove(tb->root_switch)
                                        tb->root_switch = NULL
                                      mutex_unlock(&tb->lock)
    mutex_lock(&tb->lock)
    ...
    /* without checking ->root_switch */
    tb_free_unplugged_xdomains(tb->root_switch)
    mutex_unlock(&tb->lock)

Commit a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without
holding tb->lock") doesn't seem right to move tb_free_unplugged_xdomains()
out of the &tb->lock section and the check for tb->root_switch, in
particular.  It states:

  For this reason separate removing the XDomain from the topology data
  structures (where we need the lock) from unregistering the device from
  the bus (where remove callbacks of the drivers are being called).

tb_free_unplugged_xdomains() belongs to the former group of functions
requiring the lock.  And it also calls tb_xdomain_remove() which should
only be called with &tb->lock held.

Found by Linux Verification Center (linuxtesting.org) with Svace static
analysis tool.

Fixes: a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without holding tb->lock")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

8 files changed, 641 insertions, 0 deletions

diff --git a/lib/math/tests/Makefile b/lib/math/tests/Makefile
new file mode 100644
index 000000000..85e1ad59f
--- /dev/null
+++ b/lib/math/tests/Makefile
@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+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-$(CONFIG_POLYNOMIAL_KUNIT_TEST)	+= polynomial_kunit.o
+obj-$(CONFIG_PRIME_NUMBERS_KUNIT_TEST)	+= prime_numbers_kunit.o
+obj-$(CONFIG_RATIONAL_KUNIT_TEST)	+= rational_kunit.o
diff --git a/lib/math/tests/gcd_kunit.c b/lib/math/tests/gcd_kunit.c
new file mode 100644
index 000000000..ede188358
--- /dev/null
+++ b/lib/math/tests/gcd_kunit.c
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <kunit/test.h>
+#include <linux/gcd.h>
+#include <linux/limits.h>
+
+struct test_case_params {
+	unsigned long val1;
+	unsigned long val2;
+	unsigned long expected_result;
+	const char *name;
+};
+
+static const struct test_case_params params[] = {
+	{ 48, 18, 6, "GCD of 48 and 18" },
+	{ 18, 48, 6, "GCD of 18 and 48" },
+	{ 56, 98, 14, "GCD of 56 and 98" },
+	{ 17, 13, 1, "Coprime numbers" },
+	{ 101, 103, 1, "Coprime numbers" },
+	{ 270, 192, 6, "GCD of 270 and 192" },
+	{ 0, 5, 5, "GCD with zero" },
+	{ 7, 0, 7, "GCD with zero reversed" },
+	{ 36, 36, 36, "GCD of identical numbers" },
+	{ ULONG_MAX, 1, 1, "GCD of max ulong and 1" },
+	{ ULONG_MAX, ULONG_MAX, ULONG_MAX, "GCD of max ulong values" },
+};
+
+static void get_desc(const struct test_case_params *tc, char *desc)
+{
+	strscpy(desc, tc->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+KUNIT_ARRAY_PARAM(gcd, params, get_desc);
+
+static void gcd_test(struct kunit *test)
+{
+	const struct test_case_params *tc = (const struct test_case_params *)test->param_value;
+
+	KUNIT_EXPECT_EQ(test, tc->expected_result, gcd(tc->val1, tc->val2));
+}
+
+static struct kunit_case math_gcd_test_cases[] = {
+	KUNIT_CASE_PARAM(gcd_test, gcd_gen_params),
+	{}
+};
+
+static struct kunit_suite gcd_test_suite = {
+	.name = "math-gcd",
+	.test_cases = math_gcd_test_cases,
+};
+
+kunit_test_suite(gcd_test_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("math.gcd KUnit test suite");
+MODULE_AUTHOR("Yu-Chun Lin <eleanor15x@gmail.com>");
diff --git a/lib/math/tests/int_log_kunit.c b/lib/math/tests/int_log_kunit.c
new file mode 100644
index 000000000..14e854146
--- /dev/null
+++ b/lib/math/tests/int_log_kunit.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <kunit/test.h>
+#include <linux/int_log.h>
+
+struct test_case_params {
+	u32 value;
+	unsigned int expected_result;
+	const char *name;
+};
+
+
+/* The expected result takes into account the log error */
+static const struct test_case_params intlog2_params[] = {
+	{0, 0, "Log base 2 of 0"},
+	{1, 0, "Log base 2 of 1"},
+	{2, 16777216, "Log base 2 of 2"},
+	{3, 26591232, "Log base 2 of 3"},
+	{4, 33554432, "Log base 2 of 4"},
+	{8, 50331648, "Log base 2 of 8"},
+	{16, 67108864, "Log base 2 of 16"},
+	{32, 83886080, "Log base 2 of 32"},
+	{U32_MAX, 536870911, "Log base 2 of MAX"},
+};
+
+static const struct test_case_params intlog10_params[] = {
+	{0, 0, "Log base 10 of 0"},
+	{1, 0, "Log base 10 of 1"},
+	{6, 13055203, "Log base 10 of 6"},
+	{10, 16777225, "Log base 10 of 10"},
+	{100, 33554450, "Log base 10 of 100"},
+	{1000, 50331675, "Log base 10 of 1000"},
+	{10000, 67108862, "Log base 10 of 10000"},
+	{U32_MAX, 161614247, "Log base 10 of MAX"}
+};
+
+static void get_desc(const struct test_case_params *tc, char *desc)
+{
+	strscpy(desc, tc->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+
+KUNIT_ARRAY_PARAM(intlog2, intlog2_params, get_desc);
+
+static void intlog2_test(struct kunit *test)
+{
+	const struct test_case_params *tc = (const struct test_case_params *)test->param_value;
+
+	KUNIT_EXPECT_EQ(test, tc->expected_result, intlog2(tc->value));
+}
+
+KUNIT_ARRAY_PARAM(intlog10, intlog10_params, get_desc);
+
+static void intlog10_test(struct kunit *test)
+{
+	const struct test_case_params *tc = (const struct test_case_params *)test->param_value;
+
+	KUNIT_EXPECT_EQ(test, tc->expected_result, intlog10(tc->value));
+}
+
+static struct kunit_case math_int_log_test_cases[] = {
+	KUNIT_CASE_PARAM(intlog2_test, intlog2_gen_params),
+	KUNIT_CASE_PARAM(intlog10_test, intlog10_gen_params),
+	{}
+};
+
+static struct kunit_suite int_log_test_suite = {
+	.name = "math-int_log",
+	.test_cases =  math_int_log_test_cases,
+};
+
+kunit_test_suites(&int_log_test_suite);
+
+MODULE_DESCRIPTION("math.int_log KUnit test suite");
+MODULE_LICENSE("GPL");
diff --git a/lib/math/tests/int_pow_kunit.c b/lib/math/tests/int_pow_kunit.c
new file mode 100644
index 000000000..34b33677d
--- /dev/null
+++ b/lib/math/tests/int_pow_kunit.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <kunit/test.h>
+#include <linux/math.h>
+
+struct test_case_params {
+	u64 base;
+	unsigned int exponent;
+	u64 expected_result;
+	const char *name;
+};
+
+static const struct test_case_params params[] = {
+	{ 64, 0, 1, "Power of zero" },
+	{ 64, 1, 64, "Power of one"},
+	{ 0, 5, 0, "Base zero" },
+	{ 1, 64, 1, "Base one" },
+	{ 2, 2, 4, "Two squared"},
+	{ 2, 3, 8, "Two cubed"},
+	{ 5, 5, 3125, "Five raised to the fifth power" },
+	{ U64_MAX, 1, U64_MAX, "Max base" },
+	{ 2, 63, 9223372036854775808ULL, "Large result"},
+};
+
+static void get_desc(const struct test_case_params *tc, char *desc)
+{
+	strscpy(desc, tc->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+KUNIT_ARRAY_PARAM(int_pow, params, get_desc);
+
+static void int_pow_test(struct kunit *test)
+{
+	const struct test_case_params *tc = (const struct test_case_params *)test->param_value;
+
+	KUNIT_EXPECT_EQ(test, tc->expected_result, int_pow(tc->base, tc->exponent));
+}
+
+static struct kunit_case math_int_pow_test_cases[] = {
+	KUNIT_CASE_PARAM(int_pow_test, int_pow_gen_params),
+	{}
+};
+
+static struct kunit_suite int_pow_test_suite = {
+	.name = "math-int_pow",
+	.test_cases = math_int_pow_test_cases,
+};
+
+kunit_test_suites(&int_pow_test_suite);
+
+MODULE_DESCRIPTION("math.int_pow KUnit test suite");
+MODULE_LICENSE("GPL");
diff --git a/lib/math/tests/int_sqrt_kunit.c b/lib/math/tests/int_sqrt_kunit.c
new file mode 100644
index 000000000..1798e1312
--- /dev/null
+++ b/lib/math/tests/int_sqrt_kunit.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <kunit/test.h>
+#include <linux/limits.h>
+#include <linux/math.h>
+#include <linux/module.h>
+#include <linux/string.h>
+
+struct test_case_params {
+	unsigned long x;
+	unsigned long expected_result;
+	const char *name;
+};
+
+static const struct test_case_params params[] = {
+	{ 0, 0, "edge case: square root of 0" },
+	{ 1, 1, "perfect square: square root of 1" },
+	{ 2, 1, "non-perfect square: square root of 2" },
+	{ 3, 1, "non-perfect square: square root of 3" },
+	{ 4, 2, "perfect square: square root of 4" },
+	{ 5, 2, "non-perfect square: square root of 5" },
+	{ 6, 2, "non-perfect square: square root of 6" },
+	{ 7, 2, "non-perfect square: square root of 7" },
+	{ 8, 2, "non-perfect square: square root of 8" },
+	{ 9, 3, "perfect square: square root of 9" },
+	{ 15, 3, "non-perfect square: square root of 15 (N-1 from 16)" },
+	{ 16, 4, "perfect square: square root of 16" },
+	{ 17, 4, "non-perfect square: square root of 17 (N+1 from 16)" },
+	{ 80, 8, "non-perfect square: square root of 80 (N-1 from 81)" },
+	{ 81, 9, "perfect square: square root of 81" },
+	{ 82, 9, "non-perfect square: square root of 82 (N+1 from 81)" },
+	{ 255, 15, "non-perfect square: square root of 255 (N-1 from 256)" },
+	{ 256, 16, "perfect square: square root of 256" },
+	{ 257, 16, "non-perfect square: square root of 257 (N+1 from 256)" },
+	{ 2147483648, 46340, "large input: square root of 2147483648" },
+	{ 4294967295, 65535, "edge case: ULONG_MAX for 32-bit" },
+};
+
+static void get_desc(const struct test_case_params *tc, char *desc)
+{
+	strscpy(desc, tc->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+KUNIT_ARRAY_PARAM(int_sqrt, params, get_desc);
+
+static void int_sqrt_test(struct kunit *test)
+{
+	const struct test_case_params *tc = (const struct test_case_params *)test->param_value;
+
+	KUNIT_EXPECT_EQ(test, tc->expected_result, int_sqrt(tc->x));
+}
+
+static struct kunit_case math_int_sqrt_test_cases[] = {
+	KUNIT_CASE_PARAM(int_sqrt_test, int_sqrt_gen_params),
+	{}
+};
+
+static struct kunit_suite int_sqrt_test_suite = {
+	.name = "math-int_sqrt",
+	.test_cases = math_int_sqrt_test_cases,
+};
+
+kunit_test_suites(&int_sqrt_test_suite);
+
+MODULE_DESCRIPTION("math.int_sqrt KUnit test suite");
+MODULE_LICENSE("GPL");
diff --git a/lib/math/tests/polynomial_kunit.c b/lib/math/tests/polynomial_kunit.c
new file mode 100644
index 000000000..ef443b57f
--- /dev/null
+++ b/lib/math/tests/polynomial_kunit.c
@@ -0,0 +1,270 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <kunit/test.h>
+#include <linux/polynomial.h>
+
+struct polynomial_test_param {
+	const struct polynomial *poly;
+	long data;
+	long expected;
+	const char *name;
+};
+
+/* f(x) = 5 */
+static const struct polynomial poly_constant = {
+	.total_divider = 1,
+	.terms = {
+		{0, 5, 1, 1},
+	}
+};
+
+/* f(x) = 2x^2 + 3x + 5 */
+static const struct polynomial poly_simple = {
+	.total_divider = 1,
+	.terms = {
+		{2, 2, 1, 1},
+		{1, 3, 1, 1},
+		{0, 5, 1, 1},
+	}
+};
+
+/* f(x) = -5x + 100 */
+static const struct polynomial poly_negative_coef = {
+	.total_divider = 1,
+	.terms = {
+		{1, -5, 1, 1},
+		{0, 100, 1, 1},
+	}
+};
+
+/* f(x) = (150x + 50) / 10 */
+static const struct polynomial poly_total_divider = {
+	.total_divider = 10,
+	.terms = {
+		{1, 150, 1, 1},
+		{0,  50, 1, 1},
+	}
+};
+
+/*
+ * f(x) = x / 2
+ * divider=2 applied once per multiply: mult_frac(coef, data, 2) = coef*data/2
+ */
+static const struct polynomial poly_step_divider = {
+	.total_divider = 1,
+	.terms = {
+		{1, 1, 2, 1},
+		{0, 0, 1, 1},
+	}
+};
+
+/*
+ * f(x) = (100/500) * x^2 = 0.2 * x^2
+ * Encoded as coef=100, divider=10, divider_leftover=5:
+ *   denom = 10^2 * 5 = 500
+ */
+static const struct polynomial poly_leftover = {
+	.total_divider = 1,
+	.terms = {
+		{2, 100, 10, 5},
+		{0,   0,  1, 1},
+	}
+};
+
+/*
+ * f(x) = 2x^3  (single high-degree term, no constant)
+ * Used to exercise the power loop alone.
+ */
+static const struct polynomial poly_cubic = {
+	.total_divider = 1,
+	.terms = {
+		{3, 2, 1, 1},
+		{0, 0, 1, 1},
+	}
+};
+
+/*
+ * f(x) = 4x + 1  with a zero-coefficient quadratic term.
+ * The deg-2 term contributes nothing regardless of input.
+ */
+static const struct polynomial poly_zero_coef = {
+	.total_divider = 1,
+	.terms = {
+		{2, 0, 1, 1},
+		{1, 4, 1, 1},
+		{0, 1, 1, 1},
+	}
+};
+
+/*
+ * f(x) = 9  with total_divider = 0.
+ * The implementation treats 0 as 1 via `total_divider ?: 1`, so the
+ * result must equal the constant term unchanged.
+ */
+static const struct polynomial poly_zero_total_divider = {
+	.total_divider = 0,
+	.terms = {
+		{0, 9, 1, 1},
+	}
+};
+
+
+static const struct polynomial_test_param test_params[] = {
+	{
+		.poly     = &poly_constant,
+		.data     = 0,
+		.expected = 5,
+		.name     = "Constant polynomial at x=0",
+	},
+	{
+		.poly     = &poly_constant,
+		.data     = 42,
+		.expected = 5,
+		.name     = "Constant polynomial is independent of input",
+	},
+	{
+		.poly     = &poly_simple,
+		.data     = 0,
+		.expected = 5,	/* zero input collapses all power terms */
+		.name     = "Zero input yields constant term only",
+	},
+	{
+		.poly     = &poly_simple,
+		.data     = 10,
+		.expected = 235,	/* 2*100 + 3*10 + 5 */
+		.name     = "Simple quadratic at x=10",
+	},
+	{
+		.poly     = &poly_negative_coef,
+		.data     = 10,
+		.expected = 50,		/* -5*10 + 100 */
+		.name     = "Negative coefficient at x=10",
+	},
+	{
+		.poly     = &poly_negative_coef,
+		.data     = 20,
+		.expected = 0,		/* -5*20 + 100 = 0 */
+		.name     = "Negative coefficient result is zero",
+	},
+	{
+		.poly     = &poly_total_divider,
+		.data     = 3,
+		.expected = 50,		/* (150*3 + 50) / 10 = 500/10 */
+		.name     = "total_divider scales the final sum",
+	},
+	{
+		.poly     = &poly_step_divider,
+		.data     = 100,
+		.expected = 50,		/* 1*100/2 */
+		.name     = "Per-step divider halves input",
+	},
+	{
+		.poly     = &poly_leftover,
+		.data     = 30,
+		.expected = 180,	/* 100*30^2 / (10^2 * 5) = 90000/500 */
+		.name     = "divider_leftover with quadratic term",
+	},
+	/* Boundary: unit and negative-unit input */
+	{
+		/*
+		 * data=1: each mult_frac(tmp, 1, divider) strips one factor of
+		 * divider from coef per degree, so coef is left-shifted right
+		 * until intermediate precision is exhausted.
+		 * 2*1 + 3*1 + 5 = 10
+		 */
+		.poly     = &poly_simple,
+		.data     = 1,
+		.expected = 10,
+		.name     = "Boundary: data=1 (unit input)",
+	},
+	{
+		/*
+		 * data=-1: even degrees produce positive contributions,
+		 * odd degrees produce negative ones.
+		 * 2*(-1)^2 + 3*(-1) + 5 = 2 - 3 + 5 = 4
+		 */
+		.poly     = &poly_simple,
+		.data     = -1,
+		.expected = 4,
+		.name     = "Boundary: data=-1 (negative unit input)",
+	},
+
+	/* Boundary: negative non-trivial input */
+	{
+		/*
+		 * 2*(-3)^2 + 3*(-3) + 5 = 18 - 9 + 5 = 14
+		 * Verifies sign handling for negative data across all degrees.
+		 */
+		.poly     = &poly_simple,
+		.data     = -3,
+		.expected = 14,
+		.name     = "Boundary: negative data with quadratic",
+	},
+
+	/* Boundary: total_divider = 0 is treated as 1 */
+	{
+		.poly     = &poly_zero_total_divider,
+		.data     = 42,
+		.expected = 9,
+		.name     = "Boundary: total_divider=0 defaults to 1",
+	},
+
+	/* Boundary: zero-coefficient high-degree term */
+	{
+		/*
+		 * The deg-2 term has coef=0, so it contributes 0 regardless
+		 * of data. Result: 0 + 4*10 + 1 = 41
+		 */
+		.poly     = &poly_zero_coef,
+		.data     = 10,
+		.expected = 41,
+		.name     = "Boundary: zero-coefficient term is inert",
+	},
+
+	/* Boundary: single high-degree term, no constant */
+	{
+		/* 2 * 5^3 = 250; also verifies the loop terminates on deg-0 */
+		.poly     = &poly_cubic,
+		.data     = 5,
+		.expected = 250,
+		.name     = "Boundary: single cubic term",
+	},
+	{
+		/* 2 * (-2)^3 = -16; odd power preserves sign of negative data */
+		.poly     = &poly_cubic,
+		.data     = -2,
+		.expected = -16,
+		.name     = "Boundary: single cubic term, negative data",
+	},
+
+};
+
+static void get_desc(const struct polynomial_test_param *param, char *desc)
+{
+	strscpy(desc, param->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+KUNIT_ARRAY_PARAM(polynomial, test_params, get_desc);
+
+static void polynomial_calc_test(struct kunit *test)
+{
+	const struct polynomial_test_param *param = test->param_value;
+
+	KUNIT_EXPECT_EQ(test, polynomial_calc(param->poly, param->data),
+			param->expected);
+}
+
+static struct kunit_case polynomial_test_cases[] = {
+	KUNIT_CASE_PARAM(polynomial_calc_test, polynomial_gen_params),
+	{}
+};
+
+static struct kunit_suite polynomial_test_suite = {
+	.name = "math-polynomial",
+	.test_cases = polynomial_test_cases,
+};
+
+kunit_test_suites(&polynomial_test_suite);
+
+MODULE_DESCRIPTION("math.polynomial_calc KUnit test suite");
+MODULE_LICENSE("GPL");
diff --git a/lib/math/tests/prime_numbers_kunit.c b/lib/math/tests/prime_numbers_kunit.c
new file mode 100644
index 000000000..55ac160c6
--- /dev/null
+++ b/lib/math/tests/prime_numbers_kunit.c
@@ -0,0 +1,57 @@
+// 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)
+{
+	struct kunit_suite *suite = ctx;
+
+	kunit_info(suite, "primes.{last=%lu, .sz=%lu, .primes[]=...x%lx} = %*pbl",
+		   p->last, p->sz, p->primes[BITS_TO_LONGS(p->sz) - 1], (int)p->sz, p->primes);
+}
+
+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");
diff --git a/lib/math/tests/rational_kunit.c b/lib/math/tests/rational_kunit.c
new file mode 100644
index 000000000..47486a95f
--- /dev/null
+++ b/lib/math/tests/rational_kunit.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <kunit/test.h>
+
+#include <linux/rational.h>
+
+struct rational_test_param {
+	unsigned long num, den;
+	unsigned long max_num, max_den;
+	unsigned long exp_num, exp_den;
+
+	const char *name;
+};
+
+static const struct rational_test_param test_parameters[] = {
+	{ 1230,	10,	100, 20,	100, 1,    "Exceeds bounds, semi-convergent term > 1/2 last term" },
+	{ 34567,100, 	120, 20,	120, 1,    "Exceeds bounds, semi-convergent term < 1/2 last term" },
+	{ 1, 30,	100, 10,	0, 1,	   "Closest to zero" },
+	{ 1, 19,	100, 10,	1, 10,     "Closest to smallest non-zero" },
+	{ 27,32,	16, 16,		11, 13,    "Use convergent" },
+	{ 1155, 7735,	255, 255,	33, 221,   "Exact answer" },
+	{ 87, 32,	70, 32,		68, 25,    "Semiconvergent, numerator limit" },
+	{ 14533, 4626,	15000, 2400,	7433, 2366, "Semiconvergent, denominator limit" },
+};
+
+static void get_desc(const struct rational_test_param *param, char *desc)
+{
+	strscpy(desc, param->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+/* Creates function rational_gen_params */
+KUNIT_ARRAY_PARAM(rational, test_parameters, get_desc);
+
+static void rational_test(struct kunit *test)
+{
+	const struct rational_test_param *param = (const struct rational_test_param *)test->param_value;
+	unsigned long n = 0, d = 0;
+
+	rational_best_approximation(param->num, param->den, param->max_num, param->max_den, &n, &d);
+	KUNIT_EXPECT_EQ(test, n, param->exp_num);
+	KUNIT_EXPECT_EQ(test, d, param->exp_den);
+}
+
+static struct kunit_case rational_test_cases[] = {
+	KUNIT_CASE_PARAM(rational_test, rational_gen_params),
+	{}
+};
+
+static struct kunit_suite rational_test_suite = {
+	.name = "rational",
+	.test_cases = rational_test_cases,
+};
+
+kunit_test_suites(&rational_test_suite);
+
+MODULE_DESCRIPTION("Rational fractions unit test");
+MODULE_LICENSE("GPL v2");