A recent commit fixing DMA-buffers on stack added a shared transfer buffer protected by a spinlock. This is broken as the USB HID request callbacks can sleep. Fix this up by replacing the spinlock with a mutex. Fixes: 1ffb3c40ffb5 ("HID: cp2112: make transfer buffers DMA capable") Cc: stable <stable@vger.kernel.org> # 4.9 Signed-off-by: Johan Hovold <johan@kernel.org> Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>