Comment 19 for bug 666828

Just saw this one as well today, on a 12.04.5 with a 3.13 kernel

Ssh, and serial console were unresponsive.

Console displayed message about jbd2 being blocked for more than 120 seconds, and then loads of other processes (apache2) blocked for 120 seconds as well (but jbd2 was the first such message chronologically)

Scrolling up and down virtual console worked.

Changing virtual consoles worked as well, login prompts were displayed on the other virtual consoles, but after entering user name and pressing return there would just hang (no output, apart user name itself)

After reboot (by killing the kvm process handling this virtual machine), logfiles showed a bunch of NUL characters (^@) before the reboot messages, and last message before these NULs was approx 2 hours before the crash.

We've been running this virtual machine for a while, and this is the first time this happened.