char: misc: add test cases

Add test cases for static and dynamic minor number allocation and
deallocation.

While at it, improve description and test suite name.

Some of the cases include:

- that static and dynamic allocation reserved the expected minors.

- that registering duplicate minors or duplicate names will fail.

- that failing to create a sysfs file (due to duplicate names) will
  deallocate the dynamic minor correctly.

- that dynamic allocation does not allocate a minor number in the static
  range.

- that there are no collisions when mixing dynamic and static allocations.

- that opening devices with various minor device numbers work.

- that registering a static number in the dynamic range won't conflict with
  a dynamic allocation.

This last test verifies the bug fixed by commit 6d04d2b554 ("misc:
misc_minor_alloc to use ida for all dynamic/misc dynamic minors") has not
regressed.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Link: https://lore.kernel.org/r/20250612-misc-dynrange-v5-1-6f35048f7273@igalia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/misc_minor_kunit.c

@@ -3,6 +3,9 @@
 #include <kunit/test-bug.h>
 #include <linux/module.h>
 #include <linux/miscdevice.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/init_syscalls.h>
 
 /* dynamic minor (2) */
 static struct miscdevice dev_dynamic_minor = {
@@ -51,19 +54,601 @@ static void kunit_misc_dynamic_minor(struct kunit *test)
 	misc_deregister(&dev_misc_dynamic_minor);
 }
 
+struct miscdev_test_case {
+	const char *str;
+	int minor;
+};
+
+static struct miscdev_test_case miscdev_test_ranges[] = {
+	{
+		.str = "lower static range, top",
+		.minor = 15,
+	},
+	{
+		.str = "upper static range, bottom",
+		.minor = 130,
+	},
+	{
+		.str = "lower static range, bottom",
+		.minor = 0,
+	},
+	{
+		.str = "upper static range, top",
+		.minor = MISC_DYNAMIC_MINOR - 1,
+	},
+};
+
+KUNIT_ARRAY_PARAM_DESC(miscdev, miscdev_test_ranges, str);
+
+static int miscdev_find_minors(struct kunit_suite *suite)
+{
+	int ret;
+	struct miscdevice miscstat = {
+		.name = "miscstat",
+	};
+	int i;
+
+	for (i = 15; i >= 0; i--) {
+		miscstat.minor = i;
+		ret = misc_register(&miscstat);
+		if (ret == 0)
+			break;
+	}
+
+	if (ret == 0) {
+		kunit_info(suite, "found misc device minor %d available\n",
+				miscstat.minor);
+		miscdev_test_ranges[0].minor = miscstat.minor;
+		misc_deregister(&miscstat);
+	} else {
+		return ret;
+	}
+
+	for (i = 128; i < MISC_DYNAMIC_MINOR; i++) {
+		miscstat.minor = i;
+		ret = misc_register(&miscstat);
+		if (ret == 0)
+			break;
+	}
+
+	if (ret == 0) {
+		kunit_info(suite, "found misc device minor %d available\n",
+				miscstat.minor);
+		miscdev_test_ranges[1].minor = miscstat.minor;
+		misc_deregister(&miscstat);
+	} else {
+		return ret;
+	}
+
+	for (i = 0; i < miscdev_test_ranges[0].minor; i++) {
+		miscstat.minor = i;
+		ret = misc_register(&miscstat);
+		if (ret == 0)
+			break;
+	}
+
+	if (ret == 0) {
+		kunit_info(suite, "found misc device minor %d available\n",
+			miscstat.minor);
+		miscdev_test_ranges[2].minor = miscstat.minor;
+		misc_deregister(&miscstat);
+	} else {
+		return ret;
+	}
+
+	for (i = MISC_DYNAMIC_MINOR - 1; i > miscdev_test_ranges[1].minor; i--) {
+		miscstat.minor = i;
+		ret = misc_register(&miscstat);
+		if (ret == 0)
+			break;
+	}
+
+	if (ret == 0) {
+		kunit_info(suite, "found misc device minor %d available\n",
+			miscstat.minor);
+		miscdev_test_ranges[3].minor = miscstat.minor;
+		misc_deregister(&miscstat);
+	}
+
+	return ret;
+}
+
+static bool is_valid_dynamic_minor(int minor)
+{
+	if (minor < 0)
+		return false;
+	if (minor == MISC_DYNAMIC_MINOR)
+		return false;
+	if (minor >= 0 && minor <= 15)
+		return false;
+	if (minor >= 128 && minor < MISC_DYNAMIC_MINOR)
+		return false;
+	return true;
+}
+
+static int miscdev_test_open(struct inode *inode, struct file *file)
+{
+	return 0;
+}
+
+static const struct file_operations miscdev_test_fops = {
+	.open	= miscdev_test_open,
+};
+
+static void __init miscdev_test_can_open(struct kunit *test, struct miscdevice *misc)
+{
+	int ret;
+	struct file *filp;
+	char *devname;
+
+	devname = kasprintf(GFP_KERNEL, "/dev/%s", misc->name);
+	ret = init_mknod(devname, S_IFCHR | 0600,
+			 new_encode_dev(MKDEV(MISC_MAJOR, misc->minor)));
+	if (ret != 0)
+		KUNIT_FAIL(test, "failed to create node\n");
+
+	filp = filp_open(devname, O_RDONLY, 0);
+	if (IS_ERR_OR_NULL(filp))
+		KUNIT_FAIL(test, "failed to open misc device: %ld\n", PTR_ERR(filp));
+	else
+		fput(filp);
+
+	init_unlink(devname);
+	kfree(devname);
+}
+
+static void __init miscdev_test_static_basic(struct kunit *test)
+{
+	struct miscdevice misc_test = {
+		.name = "misc_test",
+		.fops = &miscdev_test_fops,
+	};
+	int ret;
+	const struct miscdev_test_case *params = test->param_value;
+
+	misc_test.minor = params->minor;
+
+	ret = misc_register(&misc_test);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_EQ(test, misc_test.minor, params->minor);
+
+	if (ret == 0) {
+		miscdev_test_can_open(test, &misc_test);
+		misc_deregister(&misc_test);
+	}
+}
+
+static void __init miscdev_test_dynamic_basic(struct kunit *test)
+{
+	struct miscdevice misc_test = {
+		.minor = MISC_DYNAMIC_MINOR,
+		.name = "misc_test",
+		.fops = &miscdev_test_fops,
+	};
+	int ret;
+
+	ret = misc_register(&misc_test);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(misc_test.minor));
+
+	if (ret == 0) {
+		miscdev_test_can_open(test, &misc_test);
+		misc_deregister(&misc_test);
+	}
+}
+
+static void miscdev_test_twice(struct kunit *test)
+{
+	struct miscdevice misc_test = {
+		.name = "misc_test",
+		.fops = &miscdev_test_fops,
+	};
+	int ret;
+	const struct miscdev_test_case *params = test->param_value;
+
+	misc_test.minor = params->minor;
+
+	ret = misc_register(&misc_test);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_EQ(test, misc_test.minor, params->minor);
+	if (ret == 0)
+		misc_deregister(&misc_test);
+
+	ret = misc_register(&misc_test);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_EQ(test, misc_test.minor, params->minor);
+	if (ret == 0)
+		misc_deregister(&misc_test);
+}
+
+static void miscdev_test_duplicate_minor(struct kunit *test)
+{
+	struct miscdevice misc1 = {
+		.name = "misc1",
+		.fops = &miscdev_test_fops,
+	};
+	struct miscdevice misc2 = {
+		.name = "misc2",
+		.fops = &miscdev_test_fops,
+	};
+	int ret;
+	const struct miscdev_test_case *params = test->param_value;
+
+	misc1.minor = params->minor;
+	misc2.minor = params->minor;
+
+	ret = misc_register(&misc1);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_EQ(test, misc1.minor, params->minor);
+
+	ret = misc_register(&misc2);
+	KUNIT_EXPECT_EQ(test, ret, -EBUSY);
+	if (ret == 0)
+		misc_deregister(&misc2);
+
+	misc_deregister(&misc1);
+}
+
+static void miscdev_test_duplicate_name(struct kunit *test)
+{
+	struct miscdevice misc1 = {
+		.minor = MISC_DYNAMIC_MINOR,
+		.name = "misc1",
+		.fops = &miscdev_test_fops,
+	};
+	struct miscdevice misc2 = {
+		.minor = MISC_DYNAMIC_MINOR,
+		.name = "misc1",
+		.fops = &miscdev_test_fops,
+	};
+	int ret;
+
+	ret = misc_register(&misc1);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(misc1.minor));
+
+	ret = misc_register(&misc2);
+	KUNIT_EXPECT_EQ(test, ret, -EEXIST);
+	if (ret == 0)
+		misc_deregister(&misc2);
+
+	misc_deregister(&misc1);
+}
+
+/*
+ * Test that after a duplicate name failure, the reserved minor number is
+ * freed to be allocated next.
+ */
+static void miscdev_test_duplicate_name_leak(struct kunit *test)
+{
+	struct miscdevice misc1 = {
+		.minor = MISC_DYNAMIC_MINOR,
+		.name = "misc1",
+		.fops = &miscdev_test_fops,
+	};
+	struct miscdevice misc2 = {
+		.minor = MISC_DYNAMIC_MINOR,
+		.name = "misc1",
+		.fops = &miscdev_test_fops,
+	};
+	struct miscdevice misc3 = {
+		.minor = MISC_DYNAMIC_MINOR,
+		.name = "misc3",
+		.fops = &miscdev_test_fops,
+	};
+	int ret;
+	int dyn_minor;
+
+	ret = misc_register(&misc1);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(misc1.minor));
+
+	/*
+	 * Find out what is the next minor number available.
+	 */
+	ret = misc_register(&misc3);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(misc3.minor));
+	dyn_minor = misc3.minor;
+	misc_deregister(&misc3);
+	misc3.minor = MISC_DYNAMIC_MINOR;
+
+	ret = misc_register(&misc2);
+	KUNIT_EXPECT_EQ(test, ret, -EEXIST);
+	if (ret == 0)
+		misc_deregister(&misc2);
+
+	/*
+	 * Now check that we can still get the same minor we found before.
+	 */
+	ret = misc_register(&misc3);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(misc3.minor));
+	KUNIT_EXPECT_EQ(test, misc3.minor, dyn_minor);
+	misc_deregister(&misc3);
+
+	misc_deregister(&misc1);
+}
+
+/*
+ * Try to register a static minor with a duplicate name. That might not
+ * deallocate the minor, preventing it from being used again.
+ */
+static void miscdev_test_duplicate_error(struct kunit *test)
+{
+	struct miscdevice miscdyn = {
+		.minor = MISC_DYNAMIC_MINOR,
+		.name = "name1",
+		.fops = &miscdev_test_fops,
+	};
+	struct miscdevice miscstat = {
+		.name = "name1",
+		.fops = &miscdev_test_fops,
+	};
+	struct miscdevice miscnew = {
+		.name = "name2",
+		.fops = &miscdev_test_fops,
+	};
+	int ret;
+	const struct miscdev_test_case *params = test->param_value;
+
+	miscstat.minor = params->minor;
+	miscnew.minor = params->minor;
+
+	ret = misc_register(&miscdyn);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(miscdyn.minor));
+
+	ret = misc_register(&miscstat);
+	KUNIT_EXPECT_EQ(test, ret, -EEXIST);
+	if (ret == 0)
+		misc_deregister(&miscstat);
+
+	ret = misc_register(&miscnew);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_EQ(test, miscnew.minor, params->minor);
+	if (ret == 0)
+		misc_deregister(&miscnew);
+
+	misc_deregister(&miscdyn);
+}
+
+static void __init miscdev_test_dynamic_only_range(struct kunit *test)
+{
+	int ret;
+	struct miscdevice *miscdev;
+	const int dynamic_minors = 256;
+	int i;
+
+	miscdev = kunit_kmalloc_array(test, dynamic_minors,
+					sizeof(struct miscdevice),
+					GFP_KERNEL | __GFP_ZERO);
+
+	for (i = 0; i < dynamic_minors; i++) {
+		miscdev[i].minor = MISC_DYNAMIC_MINOR;
+		miscdev[i].name = kasprintf(GFP_KERNEL, "misc_test%d", i);
+		miscdev[i].fops = &miscdev_test_fops;
+		ret = misc_register(&miscdev[i]);
+		if (ret != 0)
+			break;
+		/*
+		 * This is the bug we are looking for!
+		 * We asked for a dynamic minor and got a minor in the static range space.
+		 */
+		if (miscdev[i].minor >= 0 && miscdev[i].minor <= 15) {
+			KUNIT_FAIL(test, "misc_register allocated minor %d\n", miscdev[i].minor);
+			i++;
+			break;
+		}
+		KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(miscdev[i].minor));
+	}
+
+	for (i--; i >= 0; i--) {
+		miscdev_test_can_open(test, &miscdev[i]);
+		misc_deregister(&miscdev[i]);
+		kfree_const(miscdev[i].name);
+	}
+
+	KUNIT_EXPECT_EQ(test, ret, 0);
+}
+
+static void __init miscdev_test_collision(struct kunit *test)
+{
+	int ret;
+	struct miscdevice *miscdev;
+	struct miscdevice miscstat = {
+		.name = "miscstat",
+		.fops = &miscdev_test_fops,
+	};
+	const int dynamic_minors = 256;
+	int i;
+
+	miscdev = kunit_kmalloc_array(test, dynamic_minors,
+					sizeof(struct miscdevice),
+					GFP_KERNEL | __GFP_ZERO);
+
+	miscstat.minor = miscdev_test_ranges[0].minor;
+	ret = misc_register(&miscstat);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+	KUNIT_EXPECT_EQ(test, miscstat.minor, miscdev_test_ranges[0].minor);
+
+	for (i = 0; i < dynamic_minors; i++) {
+		miscdev[i].minor = MISC_DYNAMIC_MINOR;
+		miscdev[i].name = kasprintf(GFP_KERNEL, "misc_test%d", i);
+		miscdev[i].fops = &miscdev_test_fops;
+		ret = misc_register(&miscdev[i]);
+		if (ret != 0)
+			break;
+		KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(miscdev[i].minor));
+	}
+
+	for (i--; i >= 0; i--) {
+		miscdev_test_can_open(test, &miscdev[i]);
+		misc_deregister(&miscdev[i]);
+		kfree_const(miscdev[i].name);
+	}
+
+	misc_deregister(&miscstat);
+
+	KUNIT_EXPECT_EQ(test, ret, 0);
+}
+
+static void __init miscdev_test_collision_reverse(struct kunit *test)
+{
+	int ret;
+	struct miscdevice *miscdev;
+	struct miscdevice miscstat = {
+		.name = "miscstat",
+		.fops = &miscdev_test_fops,
+	};
+	const int dynamic_minors = 256;
+	int i;
+
+	miscdev = kunit_kmalloc_array(test, dynamic_minors,
+					sizeof(struct miscdevice),
+					GFP_KERNEL | __GFP_ZERO);
+
+	for (i = 0; i < dynamic_minors; i++) {
+		miscdev[i].minor = MISC_DYNAMIC_MINOR;
+		miscdev[i].name = kasprintf(GFP_KERNEL, "misc_test%d", i);
+		miscdev[i].fops = &miscdev_test_fops;
+		ret = misc_register(&miscdev[i]);
+		if (ret != 0)
+			break;
+		KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(miscdev[i].minor));
+	}
+
+	KUNIT_EXPECT_EQ(test, ret, 0);
+
+	miscstat.minor = miscdev_test_ranges[0].minor;
+	ret = misc_register(&miscstat);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_EQ(test, miscstat.minor, miscdev_test_ranges[0].minor);
+	if (ret == 0)
+		misc_deregister(&miscstat);
+
+	for (i--; i >= 0; i--) {
+		miscdev_test_can_open(test, &miscdev[i]);
+		misc_deregister(&miscdev[i]);
+		kfree_const(miscdev[i].name);
+	}
+}
+
+static void __init miscdev_test_conflict(struct kunit *test)
+{
+	int ret;
+	struct miscdevice miscdyn = {
+		.name = "miscdyn",
+		.minor = MISC_DYNAMIC_MINOR,
+		.fops = &miscdev_test_fops,
+	};
+	struct miscdevice miscstat = {
+		.name = "miscstat",
+		.fops = &miscdev_test_fops,
+	};
+
+	ret = misc_register(&miscdyn);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(miscdyn.minor));
+
+	/*
+	 * Try to register a static minor with the same minor as the
+	 * dynamic one.
+	 */
+	miscstat.minor = miscdyn.minor;
+	ret = misc_register(&miscstat);
+	KUNIT_EXPECT_EQ(test, ret, -EBUSY);
+	if (ret == 0)
+		misc_deregister(&miscstat);
+
+	miscdev_test_can_open(test, &miscdyn);
+
+	misc_deregister(&miscdyn);
+}
+
+static void __init miscdev_test_conflict_reverse(struct kunit *test)
+{
+	int ret;
+	struct miscdevice miscdyn = {
+		.name = "miscdyn",
+		.minor = MISC_DYNAMIC_MINOR,
+		.fops = &miscdev_test_fops,
+	};
+	struct miscdevice miscstat = {
+		.name = "miscstat",
+		.fops = &miscdev_test_fops,
+	};
+
+	/*
+	 * Find the first available dynamic minor to use it as a static
+	 * minor later on.
+	 */
+	ret = misc_register(&miscdyn);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(miscdyn.minor));
+	miscstat.minor = miscdyn.minor;
+	misc_deregister(&miscdyn);
+
+	ret = misc_register(&miscstat);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_EQ(test, miscstat.minor, miscdyn.minor);
+
+	/*
+	 * Try to register a dynamic minor after registering a static minor
+	 * within the dynamic range. It should work but get a different
+	 * minor.
+	 */
+	miscdyn.minor = MISC_DYNAMIC_MINOR;
+	ret = misc_register(&miscdyn);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_NE(test, miscdyn.minor, miscstat.minor);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(miscdyn.minor));
+	if (ret == 0)
+		misc_deregister(&miscdyn);
+
+	miscdev_test_can_open(test, &miscstat);
+
+	misc_deregister(&miscstat);
+}
+
 static struct kunit_case test_cases[] = {
 	KUNIT_CASE(kunit_dynamic_minor),
 	KUNIT_CASE(kunit_static_minor),
 	KUNIT_CASE(kunit_misc_dynamic_minor),
+	KUNIT_CASE_PARAM(miscdev_test_twice, miscdev_gen_params),
+	KUNIT_CASE_PARAM(miscdev_test_duplicate_minor, miscdev_gen_params),
+	KUNIT_CASE(miscdev_test_duplicate_name),
+	KUNIT_CASE(miscdev_test_duplicate_name_leak),
+	KUNIT_CASE_PARAM(miscdev_test_duplicate_error, miscdev_gen_params),
 	{}
 };
 
 static struct kunit_suite test_suite = {
-	.name = "misc_minor_test",
+	.name = "miscdev",
+	.suite_init = miscdev_find_minors,
 	.test_cases = test_cases,
 };
 kunit_test_suite(test_suite);
 
+static struct kunit_case __refdata test_init_cases[] = {
+	KUNIT_CASE_PARAM(miscdev_test_static_basic, miscdev_gen_params),
+	KUNIT_CASE(miscdev_test_dynamic_basic),
+	KUNIT_CASE(miscdev_test_dynamic_only_range),
+	KUNIT_CASE(miscdev_test_collision),
+	KUNIT_CASE(miscdev_test_collision_reverse),
+	KUNIT_CASE(miscdev_test_conflict),
+	KUNIT_CASE(miscdev_test_conflict_reverse),
+	{}
+};
+
+static struct kunit_suite test_init_suite = {
+	.name = "miscdev_init",
+	.suite_init = miscdev_find_minors,
+	.test_cases = test_init_cases,
+};
+kunit_test_init_section_suite(test_init_suite);
+
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Vimal Agrawal");
-MODULE_DESCRIPTION("misc minor testing");
+MODULE_AUTHOR("Thadeu Lima de Souza Cascardo <cascardo@igalia.com>");
+MODULE_DESCRIPTION("Test module for misc character devices");

lib/Kconfig.debug

@@ -2506,8 +2506,8 @@ config TEST_IDA
 	tristate "Perform selftest on IDA functions"
 
 config TEST_MISC_MINOR
-	tristate "miscdevice KUnit test" if !KUNIT_ALL_TESTS
-	depends on KUNIT
+	bool "miscdevice KUnit test" if !KUNIT_ALL_TESTS
+	depends on KUNIT=y
 	default KUNIT_ALL_TESTS
 	help
 	  Kunit test for miscdevice API, specially its behavior in respect to