[PATCH v4 2/2] locking/lockdep: Testing lock class and subclass got the same name pointer

[botta633 <bottaawesome633@gmail.com>]

From: Ahmed Ehab <bottaawesome633@gmail.com>

Checking if the lockdep_map->name will change when setting the subclass.
It shouldn't change so that the lock class and subclass will have the same
name

Reported-by: <syzbot+7f4a6f7f7051474e40ad@syzkaller.appspotmail.com>
Fixes: de8f5e4f2dc1f ("lockdep: Introduce wait-type checks")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ahmed Ehab <bottaawesome633@gmail.com>
---
 lib/locking-selftest.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index 6f6a5fc85b42..aeed613799ca 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -2710,6 +2710,25 @@ static void local_lock_3B(void)
 
 }
 
+ /** 
+  * after setting the subclass the lockdep_map.name changes
+  * if we initialize a new string literal for the subclass
+  * we will have a new name pointer
+  */
+static void class_subclass_X1_name_test(void)
+{
+	printk("  --------------------------------------------------------------------------\n");
+	printk("  | class and subclass name test|\n");
+	printk("  ---------------------\n");
+	const char *name_before_setting_subclass = rwsem_X1.dep_map.name;
+	const char *name_after_setting_subclass;
+
+	WARN_ON(!rwsem_X1.dep_map.name);
+	lockdep_set_subclass(&rwsem_X1, 1);
+	name_after_setting_subclass = rwsem_X1.dep_map.name;
+	WARN_ON(name_before_setting_subclass != name_after_setting_subclass);
+}
+
 static void local_lock_tests(void)
 {
 	printk("  --------------------------------------------------------------------------\n");
@@ -2916,6 +2935,8 @@ void locking_selftest(void)
 
 	local_lock_tests();
 
+	class_subclass_X1_name_test();
+
 	print_testname("hardirq_unsafe_softirq_safe");
 	dotest(hardirq_deadlock_softirq_not_deadlock, FAILURE, LOCKTYPE_SPECIAL);
 	pr_cont("\n");
-- 
2.45.2