In the Linux kernel, the following vulnerability has been resolved: Input: uinput - fix circular locking dependency with ff-core A lockdep circular locking dependency warning can be triggered reproducibly when using a force-feedback gamepad with uinput (for example, playing ELDEN RING under Wine with a Flydigi Vader 5 controller): ff-mutex - udev-mutex - input_mutex - dev-mutex - ff-mutex The cycle is caused by four lock acquisition paths: 1. ff upload: input_ff_upload() holds ff-mutex and calls uinput_dev_upload_effect() - uinput_request_submit() - uinput_request_send(), which acquires udev-mutex. 2. device create: uinput_ioctl_handler() holds udev-mutex and calls uinput_create_device() - input_register_device(), which acquires input_mutex. 3. device register: input_register_device() holds input_mutex and calls kbd_connect() - input_register_handle(), which acquires dev-mutex. 4. evdev release: evdev_release() calls input_flush_device() under dev-mutex, which calls input_ff_flush() acquiring ff-mutex. Fix this by introducing a new state_lock spinlock to protect udev-state and udev-dev access in uinput_request_send() instead of acquiring udev-mutex. The function only needs to atomically check device state and queue an input event into the ring buffer via uinput_dev_event() -- both operations are safe under a spinlock (ktime_get_ts64() and wake_up_interruptible() do not sleep).

This breaks the ff-mutex - udev-mutex link since a spinlock is a leaf in the lock ordering and cannot form cycles with mutexes. To keep state transitions visible to uinput_request_send(), protect writes to udev-state in uinput_create_device() and uinput_destroy_device() with the same state_lock spinlock. Additionally, move init_completion(&request-done) from uinput_request_send() to uinput_request_submit() before uinput_request_reserve_slot().

Once the slot is allocated, uinput_flush_requests() may call complete() on it at any time from the destroy path, so the completion must be initialised before the request becomes visible. Lock ordering after the fix: ff-mutex - state_lock (spinlock, leaf) udev-mutex - state_lock (spinlock, leaf) udev-mutex - input_mutex - dev-mutex - ff-mutex (no back-edge)