Console writes blocking

[thumphries]

We've been observing some console writes of the form writeConsole con "My cool string\n" blocking the entire HaLVM. This is using the unthreaded runtime, though there are probably IO signals arriving from XenDevice.NIC.

Getting into the console with xl console domid and hitting RET will unblock it. This makes me suspect preProcessInput and postProcessInput. I'll try to figure out an isolated example.

[thumphries]

This is proving harder to isolate than I'd hoped. At first I factored out every call to putStr, writeConsole and family behind some runtime option in our internal project, but still found domains hanging out for a RET.

Disabling the console i.e. not calling initXenConsole was an effective (but vacuous) workaround.

There's an unhandled ringbuffer wrap-around case in Console, could be that. My failed attempts at a standalone example were all very simple and single-threaded HaLVMs, so the next step might be to run a simple HaNS appliance and hammer the console from it.