On 28.08.25 17:00, Lorenzo Stoakes wrote:

On Thu, Aug 28, 2025 at 12:01:14AM +0200, David Hildenbrand wrote:

quoted

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.

quoted

Reviewed-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: David Hildenbrand <redacted>

LGTM (apart from nit below), so:

Reviewed-by: Lorenzo Stoakes <redacted>

quoted

---
  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.

-- 
Cheers

David / dhildenb