[testing] Techniques for testing robustness

Just noticed `MADV_HWPOISON` flag for `madvise`:

> Poison the pages in the range specified by addr and length and
> handle subsequent references to those pages like a hardware memory
> corruption. This operation is available only for privileged
> (`CAP_SYS_ADMIN`) processes. This operation may result in the
> calling process receiving a `SIGBUS` and the page being unmapped.
>
> This feature is intended for _testing of memory error-handling code_;
> itis available only if the kernel was configured with
> `CONFIG_MEMORY_FAILURE`.

(the flag is enabled in Fedora kernels)