Call for Testing/Review - TTY locking

[Kyle Evans]

Hi,

I've got a patch now up for review that breaks up TTY locking a little
bit, with an eye primarily towards fixing the USB/TTY intersection
that's been known to cause some problems in userland in the past; the
pertinent change starts at usb_serial.c:633 in the below patch.

Review is located here: https://reviews.freebsd.org/D24459 -- as far
as I know, this is a complete and functional diff. I had ran it for a
couple months on one of my 3d-printer-attached machines with no
problems operating ucom under the new locking model and otherwise
using the machine.

Review and testing under tty-heavy and diverse workloads would be
greatly appreciated. Please feel free to add yourself as a reviewer on
phabricator.

Thanks,

kyle Evans