Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity_checks

[Yin, Fengwei]

On 1/5/2024 11:45 PM, David Hildenbrand wrote:
> > > vm_normal_page() works on these mappings, so we'd also have to skip rmap
> > > code when unmapping these pages etc. Maybe that's the whole reason we
> > > have the rmap handling here: to not special-case the unmap path.
> >
> > vm_insert_page() will set VM_MIXEDMAP and vm_normal_page() will skip
> > the page if CONFIG_ARCH_HAS_PTE_SPECIAL is enabled (it's enabled for
> > x86).  So the unmap path will skip these kind of folios?
>
> I think we run into the
>      if (likely(!pte_special(pte)))
>          goto check_pfn;
>
> first and return these folios. That also matches the comment of 
> vm_normal_page: "VM_MIXEDMAP mappings can likewise contain memory with 
> or without ... _all_ pages with a struct page (that is, those where 
> pfn_valid is true) are refcounted and considered normal pages by the VM."
Oh. Yes. This is the path. Thanks a lot for pointing it out to me.


Regards
Yin, Fengwei