had just installed virtualbox extension pack, then plugged in HP ScanJet 5000 scanner to virtual
machine. tried to scan; first scan failed with a driver error box in the Windows VM; then the 
scanner disappeared from USB and the host system stopped recognizing anything on the USB ports.

dmesg showed these errors:

[70452.757935] ieee80211 phy0: brcms_ops_bss_info_changed: arp filtering: enabled true, count 0 (implement)
[70453.074050] ieee80211 phy0: brcms_ops_bss_info_changed: arp filtering: enabled true, count 1 (implement)
[70592.828165] usb 1-3: reset high-speed USB device number 7 using ehci_hcd
[70601.528015] hrtimer: interrupt took 19572 ns
[70659.952139] ehci_hcd 0000:00:12.2: force halt; handshake f82bc024 00004000 00000000 -> -110
[70659.952154] ehci_hcd 0000:00:12.2: HC died; cleaning up
[70659.952207] usb 1-3: USB disconnect, device number 7
[70659.952229] usb 1-3: usbfs: usb_submit_urb returned -110

Removing/unloading the ehci_hcd module fixed the problem without a reboot:

# rmmod ehci_hcd

The driver automatically reloaded and re-recognized all USB devices; subsequent USB usage from
the virtual machine worked without difficulty (VM did need to be rebooted again though, as USB
seemed limited to USB1 speeds).

Note: sometimes ehci_hcd may stay unloaded, and all devices are limited to USB 1 speed. In this
case manually reload it with:

# modprobe ehci_hcd