> It’s the kernel. Nothing a user space library can do should ever be able to call this.

I don't follow. An application might see this kind of crash if it has a bug causing it to access a page while another thread is mapping or unmapping that page. That would be a bug in mallocng, musl or ripgrep. Or, as someone else mentioned, it could be bug in the processor's virtual memory logic that has the same effect. Why do you say it can only be a kernel bug?

It got traced to a race condition in munmap() in the kernel. The inefficient musl allocator simply triggers it more easily.