Dear mr Johan Hovold Can you reproduce this with a mainline kernel? Otherwise, you may need to bring this up with Ubuntu. -> this bug doesn't occur on Ubuntu running on pc, it only occur on raspberry. One additional thing: the bug doesn't occur with HUB: Orico, model W6ph4-u3-v1, Manufacture: VIA Labs, inc. It only occur with hub: HB-UM43 hub, Genesys Logic, Inc. This sounds like you could have a problem with the host-controller driver. What controller is the RPi4 using? -> For the Pi 4, a fully-featured host controller drives the downstream USB ports. Downstream USB is provided by a Via Labs VL805 chip - that supports two USB 2.0 ports and two USB 3.0 ports As you write above, the usb_serial_generic_close() is needed to cancel the outstanding URBs during close so you can't remove that. But my guess is that something breaks in the HCD when unlinking those URBs when connected through the hub. Do you have a stack trace from an oops? Or do things just lock up? -> I don't know how to capture stack trace? Tung pham.
