Re: [PATCH v1 10/36] mm: sanity-check maximum folio size in folio_set_order()

On Fri, Aug 29, 2025 at 12:10:30PM +0200, David Hildenbrand wrote:
> On 28.08.25 17:00, Lorenzo Stoakes wrote:
> > On Thu, Aug 28, 2025 at 12:01:14AM +0200, David Hildenbrand wrote:
> > > Let's sanity-check in folio_set_order() whether we would be trying to
> > > create a folio with an order that would make it exceed MAX_FOLIO_ORDER.
> > >
> > > This will enable the check whenever a folio/compound page is initialized
> > > through prepare_compound_head() / prepare_compound_page().
> >
> > NIT: with CONFIG_DEBUG_VM set :)
>
> Yes, will add that.

Thanks!

>
> >
> > >
> > > Reviewed-by: Zi Yan <[email protected]>
> > > Signed-off-by: David Hildenbrand <[email protected]>
> >
> > LGTM (apart from nit below), so:
> >
> > Reviewed-by: Lorenzo Stoakes <[email protected]>
> >
> > > ---
> > >   mm/internal.h | 1 +
> > >   1 file changed, 1 insertion(+)
> > >
> > > diff --git a/mm/internal.h b/mm/internal.h
> > > index 45da9ff5694f6..9b0129531d004 100644
> > > --- a/mm/internal.h
> > > +++ b/mm/internal.h
> > > @@ -755,6 +755,7 @@ static inline void folio_set_order(struct folio *folio, unsigned int order)
> > >   {
> > >   	if (WARN_ON_ONCE(!order || !folio_test_large(folio)))
> > >   		return;
> > > +	VM_WARN_ON_ONCE(order > MAX_FOLIO_ORDER);
> >
> > Given we have 'full-fat' WARN_ON*()'s above, maybe worth making this one too?
>
> The idea is that if you reach this point here, previous such checks I added
> failed. So this is the safety net, and for that VM_WARN_ON_ONCE() is
> sufficient.
>
> I think we should rather convert the WARN_ON_ONCE to VM_WARN_ON_ONCE() at
> some point, because no sane code should ever trigger that.

Ack, ok. I don't think vital for this series though!

>
> --
> Cheers
>
> David / dhildenb
>

Cheers, Lorenzo