This bug has been copied from bug #637930 and has been proposed
to be backported to 5.6 z-stream (EUS).
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.
Technical note added. If any revisions are required, please edit the "Technical Notes" field
accordingly. All revisions will be proofread by the Engineering Content Services team.
Under certain circumstances, a deadlock could occur between the khubd process of the USB stack and the modprobe of the usb-storage module. This was because the khubd process, when attempting to delete a usb device, waited for the reference count of knode_bus to be of value 0. However, modprobe, when loading the usb-storage module, scans all USB devices and increments the reference count, preventing the khubd process to continue. With this update, the underlying source code has been modified to address this issue, and a deadlock no longer occurs in the aforementioned case.