Re: [patch 1/1] mm/debug: add tests validating architecture page table helpers

[Linus Torvalds <torvalds@linux-foundation.org>]

On Sun, Apr 12, 2020 at 12:42 AM Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> Test page table pages are allocated from system memory with required size
> and alignments.  The mapped pfns at page table levels are derived from a
> real pfn representing a valid kernel text symbol.  This test gets called
> inside kernel_init() right after async_synchronize_full().

This last part makes absolutely zero sense to me.

Why would it be done before the machine is properly up? Why isn't this
just a module with a module_init? What makes this test so important
and magical that it has to be done during early boot?

So not applied, particularly since this apparently caused problems. We
don't randomly break the boot, which is fragile anyway, just for a
test that doesn't look like it should be boot-specific to me.

If it wants a new clean mm, it should just do a fork. And do so
_looong_ long after boot.

                Linus