From: Pankaj Raghav <p.raghav@samsung.com>

split_huge_page_to_list_[to_order](), split_huge_page() and
try_folio_split() return 0 on success and error codes on failure.

When THP is disabled, these functions return 0 indicating success even
though an error code should be returned as it is not possible to split a
folio when THP is disabled.

Make all these functions return -EINVAL to indicate failure instead of
0. As large folios depend on CONFIG_THP, issue warning as this function
should not be called without a large folio.

Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Acked-by: Kiryl Shutsemau <kas@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202509051753.riCeG7LC-lkp@intel.com/
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
---
Changes since v3:
  - use VM_WARN_ON_ONCE_PAGE instead of the folio version in functions
    that take a page.

Changes since v2:
  - use page_folio(page) directly in VM_WARN_ON_ONCE_FOLIO

 include/linux/huge_mm.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 7748489fde1b..cd61d2b789ec 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -553,22 +553,26 @@ static inline int
 split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 		unsigned int new_order)
 {
-	return 0;
+	VM_WARN_ON_ONCE_PAGE(1, page);
+	return -EINVAL;
 }
 static inline int split_huge_page(struct page *page)
 {
-	return 0;
+	VM_WARN_ON_ONCE_PAGE(1, page);
+	return -EINVAL;
 }
 
 static inline int split_folio_to_list(struct folio *folio, struct list_head *list)
 {
-	return 0;
+	VM_WARN_ON_ONCE_FOLIO(1, folio);
+	return -EINVAL;
 }
 
 static inline int try_folio_split(struct folio *folio, struct page *page,
 		struct list_head *list)
 {
-	return 0;
+	VM_WARN_ON_ONCE_FOLIO(1, folio);
+	return -EINVAL;
 }
 
 static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {}

base-commit: e6b9dce0aeeb91dfc0974ab87f02454e24566182
-- 
2.50.1

On 05/09/25 8:30 PM, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
> 
> split_huge_page_to_list_[to_order](), split_huge_page() and
> try_folio_split() return 0 on success and error codes on failure.
> 
> When THP is disabled, these functions return 0 indicating success even
> though an error code should be returned as it is not possible to split a
> folio when THP is disabled.
> 
> Make all these functions return -EINVAL to indicate failure instead of
> 0. As large folios depend on CONFIG_THP, issue warning as this function
> should not be called without a large folio.
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> Acked-by: Zi Yan <ziy@nvidia.com>
> Acked-by: Kiryl Shutsemau <kas@kernel.org>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202509051753.riCeG7LC-lkp@intel.com/
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
> Changes since v3:
>   - use VM_WARN_ON_ONCE_PAGE instead of the folio version in functions
>     that take a page.
> 
> Changes since v2:
>   - use page_folio(page) directly in VM_WARN_ON_ONCE_FOLIO
> 
>  include/linux/huge_mm.h | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 7748489fde1b..cd61d2b789ec 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -553,22 +553,26 @@ static inline int
>  split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>  		unsigned int new_order)
>  {
> -	return 0;
> +	VM_WARN_ON_ONCE_PAGE(1, page);
> +	return -EINVAL;
>  }
>  static inline int split_huge_page(struct page *page)
>  {
> -	return 0;
> +	VM_WARN_ON_ONCE_PAGE(1, page);
> +	return -EINVAL;
>  }
>  
>  static inline int split_folio_to_list(struct folio *folio, struct list_head *list)
>  {
> -	return 0;
> +	VM_WARN_ON_ONCE_FOLIO(1, folio);
> +	return -EINVAL;
>  }
>  
>  static inline int try_folio_split(struct folio *folio, struct page *page,
>  		struct list_head *list)
>  {
> -	return 0;
> +	VM_WARN_ON_ONCE_FOLIO(1, folio);
> +	return -EINVAL;
>  }
>  
>  static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {}
> 
> base-commit: e6b9dce0aeeb91dfc0974ab87f02454e24566182

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>