[CentOS-virt] 100% load on core after physically removing USB storage from host

Emmanuel Noobadmin centos.admin at gmail.com
Tue Jun 12 01:25:23 EDT 2012

I encountered a problem after removing a USB flash drive using virtual
machine manager, I
notice that the core assigned to the VM guest goes up to 100% load.
Within the guest itself, there is no significant activity.

This also prompted me to look at the other physical machine from which
I used the USB flash drive to transfer files. And it was also
exhibiting the same problem.

Installed versions are
on CentOS 6.2, 2.6.32-220.17.1.el6.x86_64 (Intel C204 PCH)

There are no error messages in the log files and things seem to be
working except for the fully loaded core.

After some testing, the only steps needed are
1. VMM add physical host usb device -> select storage to guest
2. VMM remove hardware
3. Physically remove the USB storage from the host, thread/core
assigned to guest goes 100%

Repeating the same steps without restarting the guest causes cpu
utilization to drop back to normal for about a second or so before
going back up again.

Problem goes away if I restart the guest. There don't seem to be anything
related on RHEL bugtrack except one related to hotplug/unplugging a
USB controller more
than 1000 times.

Is this is a bug or there is actually something else I am supposed to
do before removing a physical device from a guest?

Also is there anyway I get the core/thread back to normal without
restarting the guest?

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