https://bugzilla.kernel.org/show_bug.cgi?id=214001
--- Comment #5 from Linux_Chemist (untaintableangel@hotmail.co.uk) --- I can sense you're a smart cookie, Duncan, I've enjoyed this little tete a tete.
I think this bug has been addressed, it's just not been mentioned yet (see the following into mainline): https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/dr...
" This changes it so that if creation of TTM's debugfs root directory fails, then no biggie: keep calm and carry on."
Will test it out as soon as I can and comment/adjust the bug report.