Re: [PATCH 01/13] mm: Update ptep_get_lockless()s comment

[Peter Zijlstra]

On Sun, Oct 30, 2022 at 06:47:23PM -0700, Linus Torvalds wrote:

> Also, it's worth noting that zap_pte_range() does this sanity test:
> 
>                         if (unlikely(page_mapcount(page) < 0))
>                                 print_bad_pte(vma, addr, ptent, page);
> 
> and that is likely worthless now (because it hasn't actually
> decremented the mapcount yet). I didn't remove it, because I wasn't
> sure which option was best:
> 
>  (a) just remove it entirely
> 
>  (b) change the "< 0" to "<= 0"
> 
>  (c) move it to clean_and_free_pages_and_swap_cache() that actually
> does the page_zap_pte_rmap() now.

I'm leaning towards (c); simply because the error case is so terrifying
I feel we should check for it (and I do have vague memories of us
actually hitting something like this in the very distant past).