From: Zijun Hu <zijun.hu@oss.qualcomm.com>

Add a case to test reentry about requesting dynamic minor:

1) Provide Both @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 registered successfully.

Signed-off-by: Zijun Hu <zijun.hu@oss.qualcomm.com>
---
 drivers/char/misc_minor_kunit.c | 44 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/drivers/char/misc_minor_kunit.c b/drivers/char/misc_minor_kunit.c
index 81e2ef488a6f6ae7138c7dd8bcbeffe38aa65933..9f1f77c04f9f1be56bc94cab4127ecb941e128b2 100644
--- a/drivers/char/misc_minor_kunit.c
+++ b/drivers/char/misc_minor_kunit.c
@@ -602,6 +602,49 @@ static void __init 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 __init 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),
 	{}
 };
 

-- 
2.34.1

Hi Zijun,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 626e89412dfb88766d90d842af4d9ec432d8526f]

url:    https://github.com/intel-lab-lkp/linux/commits/Zijun-Hu/char-misc-Move-drivers-misc-misc_minor_kunit-c-to-drivers-char/20250702-202131
base:   626e89412dfb88766d90d842af4d9ec432d8526f
patch link:    https://lore.kernel.org/r/20250702-rfc_miscdev-v3-4-d8925de7893d%40oss.qualcomm.com
patch subject: [PATCH v3 4/8] char: misc: Add a reentry test case about dynamic minor request
config: powerpc64-randconfig-002-20250704 (https://download.01.org/0day-ci/archive/20250704/202507042031.3gfceqb3-lkp@intel.com/config)
compiler: powerpc64-linux-gcc (GCC) 10.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250704/202507042031.3gfceqb3-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202507042031.3gfceqb3-lkp@intel.com/

All warnings (new ones prefixed by >>, old ones prefixed by <<):

WARNING: modpost: vmlinux: section mismatch in reference: hash_debug_pagealloc_alloc_slots+0x98 (section: .text) -> memblock_alloc_try_nid (section: .init.text)
WARNING: modpost: vmlinux: section mismatch in reference: test_cases+0x60 (section: .data) -> miscdev_test_invalid_input (section: .init.text)
>> WARNING: modpost: vmlinux: section mismatch in reference: test_cases+0x180 (section: .data) -> miscdev_test_dynamic_reentry (section: .init.text)

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki