On Fri, May 25, 2012 at 4:36 PM, Robert P. J. Day [off-list ref] wrote:

?reading a course outline and there's a reference to "lockless
ioctls". ?no idea what that is, and google doesn't make it any
clearer:

http://www.google.ca/#hl=en&sclient=psy-ab&q=%22lockless+ioctl%22&oq=%22lockless+ioctl%22&aq=f&aqi=&aql=&gs_l=hp.3...1480.3588.0.3748.16.16.0.0.0.0.221.1642.10j5j1.16.0...0.0.noPYe58Fdcg&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=f4bd7f4bc3a9df92&biw=1060&bih=925

did such a thing ever exist?

All ioctls are unlocked, now that the BKL is gone.  You can read more
about it, including relevant lwn links, at [1].

[1] http://unix.stackexchange.com/questions/4711/what-is-the-difference-between-ioctl-unlocked-ioctl-and-compat-ioctl

HTH,
Vlad