Comment 142 for bug 1505564

Well, yes I agree, it does look like the serial port causing the softlockup is probably separate - but caused by - the nbd closed socket errors. However, the serial port output definitely shouldn't be causing a softlockup - no matter how much data it has to send, the serial port driver in the kernel should be scheduling itself during operation, so that it doesn't hog a single cpu for a long time. It's more likely that the general system "freezing" you are seeing is due to the serial port driver refusing to schedule off its cpu, and not any problem with the nbdX failure.

I'll look into the nbd code also though, to see where that error is coming from and what that problem may be.