Earlier this evening I updated our CentOS-6.2 kvm virtual host to kernel 2.6.32-220.4.1.el6. After rebooting three guests are hung. I cannot establish connections via the network (no route to host) and the virtual console is unresponsive. On two of them I was able to initiate the login process but after the password prompt the system no longer responded. On the other the system hung when I tried to run the vi editor.

The console display on each of the affected guests shows a long list of hung tasks:

task jbd2/dm-0-0:384 blocked for more than 120 seconds . . . task jbd2/dm-3-8:838 blocked for more than 120 seconfs

task master:1226 blocked for more than . . .

task miniserv.pl:1248 blocked

task pickup:29136 blocked

The lists on each guest vary somewhat but share most of the same processes being blocked. One has a postmaster task that does not display on any of the others.

I can recover from this but I want to get these guests restarted if I possibly can. Is there a way to do this? What would cause the problem?