char: misc: Add a case to test registering miscdevice again without reinitialization

For miscdevice who wants dynamic minor, add a cast to test if it can be
successfully registered again without reinitialization:

1) Provide Both miscdevice @dev_A and @dev_B want to request dynamic
   minor by initializing their minor to MISC_DYNAMIC_MINOR.

2) Register then de-register @dev_A.

3) Register @dev_B.

4) Register @dev_A again without reinitialization.

5) Check if @dev_A can be successfully registered.

Signed-off-by: Zijun Hu <zijun.hu@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250714-rfc_miscdev-v6-4-2ed949665bde@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 44 insertions, 0 deletions

diff --git a/drivers/char/misc_minor_kunit.c b/drivers/char/misc_minor_kunit.c
index 3184f383bea8..6fc8b05169c5 100644
--- a/drivers/char/misc_minor_kunit.c
+++ b/drivers/char/misc_minor_kunit.c
@@ -602,6 +602,49 @@ static void miscdev_test_invalid_input(struct kunit *test)
 		misc_deregister(&misc_test);
 }
 
+/*
+ * Verify if @miscdyn_a can still be registered successfully without
+ * reinitialization even if its minor ever owned was requested by
+ * another miscdevice such as @miscdyn_b.
+ */
+static void miscdev_test_dynamic_reentry(struct kunit *test)
+{
+	struct miscdevice miscdyn_a = {
+		.name = "miscdyn_a",
+		.minor = MISC_DYNAMIC_MINOR,
+		.fops = &miscdev_test_fops,
+	};
+	struct miscdevice miscdyn_b = {
+		.name = "miscdyn_b",
+		.minor = MISC_DYNAMIC_MINOR,
+		.fops = &miscdev_test_fops,
+	};
+	int ret, minor_a;
+
+	ret = misc_register(&miscdyn_a);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(miscdyn_a.minor));
+	minor_a = miscdyn_a.minor;
+	if (ret != 0)
+		return;
+	misc_deregister(&miscdyn_a);
+
+	ret = misc_register(&miscdyn_b);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+	KUNIT_EXPECT_EQ(test, miscdyn_b.minor, minor_a);
+	if (ret != 0)
+		return;
+
+	ret = misc_register(&miscdyn_a);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+	KUNIT_EXPECT_TRUE(test, is_valid_dynamic_minor(miscdyn_a.minor));
+	KUNIT_EXPECT_NE(test, miscdyn_a.minor, miscdyn_b.minor);
+	if (ret == 0)
+		misc_deregister(&miscdyn_a);
+
+	misc_deregister(&miscdyn_b);
+}
+
 static struct kunit_case test_cases[] = {
 	KUNIT_CASE(kunit_static_minor),
 	KUNIT_CASE(kunit_misc_dynamic_minor),
@@ -611,6 +654,7 @@ static struct kunit_case test_cases[] = {
 	KUNIT_CASE(miscdev_test_duplicate_name),
 	KUNIT_CASE(miscdev_test_duplicate_name_leak),
 	KUNIT_CASE_PARAM(miscdev_test_duplicate_error, miscdev_gen_params),
+	KUNIT_CASE(miscdev_test_dynamic_reentry),
 	{}
 };