Guess I just got lucky; the run with --logverbose 6 did eventually crash the OS.
Here’s the bug report log: http://kegel.com/linux/piglit-nvidia-bug-report.log.gz
The last two lines from piglit were
running: spec/arb_texture_rectangle/texrect_simple_arb_texrect
[3524/4261] skip: 230, pass: 796, dmesg-warn: 1, fail: 2494, dmesg-fail: 2, crash: 1
tail -f /var/log/kern.log showed:
Sep 16 09:58:14 rbb-ubu1604-3 kernel: [ 1475.867942] ext_texture_for[12354]: segfault at 0 ip 00007fcd50ebf640 sp 00007ffe6ec58058 error 4 in libc-2.23.so[7fcd50d5f000+1c0000]
(Note: I had to install xserver-xorg-legacy to get past the x server not being able to
detect my displays, so it ran setuid root just like it used to by default in ubuntu 12.04, I think.)