`mask_sdf` SIGSEGVd after printing `test result: ok`, and the workaround
was to hand the device to the process with `mem::forget` on the reading
that "dropping a wgpu device on Venus segfaults". Every part of that
except the symptom was wrong.
`rigs/gpu-probe`'s new `teardown` bin is the experiment, one variable per
mode: the same open-and-close exits 0 on the main thread and SIGSEGVs on
a spawned one; it needs no GPU work and no device, only an instance; raw
`ash` does it with no wgpu involved at all; and keeping the instance
alive fixes it. Destroying the last VkInstance makes the loader dlclose
the ICD, and Mesa's ICD here registers a pthread_key_create destructor
into its own text without `-z nodelete`, so glibc calls it through
unmapped memory when the thread exits. libtest runs every #[test] on a
spawned thread, which is the whole reason this looked like a drop bug.
`VK_LOADER_DISABLE_DYNAMIC_LIBRARY_UNLOADING=1` confirms the mechanism.
So the fix is one `wgpu::Instance` for the process -- what wgpu asks for
anyway -- and the device, queue and everything else drop normally again.
The escape and its paragraph of reasons are gone.
Also: the machine-level graphics notes duplicated in docs/RUST.md,
run-headless.sh and two source comments now point at the
`this-machine-graphics` skill, which is the only copy.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
irisandClaude Opus 5
b9924e7617