This has happened occasionally during manual runs of tast-test, and now I have a repro case for it.

If you SSH into the DUT and run this script (replace owner_id):

x=0; while [ 1 ] ; do vsh --vm_name=termina --target_container=penguin --owner_id=533dd0c6a9276e2629fa1eac6a5ccbb8eeb24d59 -- sh -c "echo 'nothing but the web ${x}' > ~/index.html"; echo ${x}; x=`expr ${x} + 1`; done

Then after a little bit it will end up hanging. If you then connect into the terminal you'll see vsh using 100% of the CPU and a defunct sh process.

Occasionally it also spits out this error:

[ERROR:utils.cc(32)] Failed to write message size to socket: Broken pipe
[ERROR:vsh_client.cc(264)] Failed to send tty window resize message

Putting the DUT under load makes this happen faster; it's also more likely to happen if there isn't another active vsh session.