kernel-side thread stack swapping

Is this really of practical use today?

I have a WIP patch which needs to temporarily store something on the
stack and should things go wrong enough it will be accessed by UMA,
which can't handle the fault nor decide to skip the access.

I can add something like td_pinstack or whatever to keep it around,
but perhaps the entire machinery can be just whacked?

-- 
Mateusz Guzik <mjguzik gmail.com>