Kingsoft Typing Pass failed to start probabilistically due to a deadlock between two threads registering and unregistering the same class. The replication scenario is as follows: |A thread (registration class) | B thread (deregistration class)| |-------------- |---------------| | NtUserRegisterClassExWOW | NtUserUnregisterClass | | create_class | -- | | -- | destroy_class | | find_shared_session_object | -- | | find failed, destroy_class | -- | | free class | -- | | -- | user_lock | | -- | remove class from list | | -- | throw exception(class has freeed by thread A) | Thread B threw an exception and will not call user_unlock. The upper layer application handled the memory access exception thrown by thread B, but due to If user_unlock is not called, the lock will remain occupied, and other threads will continue to wait when calling user_rock. -- v3: Win32u: Fixed thread safety issues with NtUserRegistClassExWOW and NtUserUnregisterClass. user32/tests: Test the thread safety of NtUserRegisterClassExWOW and NtUserUnregisterClass. https://gitlab.winehq.org/wine/wine/-/merge_requests/10271