[Qemu-devel] [BUG] qemu stuck when detach host-usb device

[linzhecheng]

Description of problem:
The guest has a host-usb device(Kingston Technology DataTraveler 100 G3/G4/SE9 
G2), which is attached
to xhci controller(on host). Qemu will stuck if I detach it from guest.

How reproducible:
100%

Steps to Reproduce:
1.            Use usb stick to copy files in guest , make it busy working.
2.            virsh detach-device vm_name usb.xml

Then qemu will stuck for 20s, I found this is because libusb_release_interface 
block for 20s.
Dmesg prints:

[35442.034861] usb 4-2.1: Disable of device-initiated U1 failed.
[35447.034993] usb 4-2.1: Disable of device-initiated U2 failed.
[35452.035131] usb 4-2.1: Set SEL for device-initiated U1 failed.
[35457.035259] usb 4-2.1: Set SEL for device-initiated U2 failed.

Is this a hardware error or software's bug?