This happens because GPU fault recovery currently leaves the process in a
totally broken state. (And all other processes that use the GPU, seemingly.)

The general approach has been to try to avoid the GPU faults in the first place
-- that will be printed before any of your other errors (i.e. before the
nv50_cal stuff).

Note that mesa 18.0 may have some relevant fixes, e.g. 

commit adcd241b563f44b2e3e92f5d840e2f617bc25836
Author: Ilia Mirkin <imirkin@alum.mit.edu>
Date:   Mon Jan 1 14:54:17 2018 -0500

    nvc0: ensure that pushbuf keeps ref to old text/tls bos

Perhaps worth a shot. (This could hit if gnome-shell were generating tons and
tons of silly shaders. Which it might be.)