Re: [PATCH] huge_memory: return -EINVAL in folio split functions when THP is disabled

[Kiryl Shutsemau]

On Tue, Sep 02, 2025 at 10:40:36AM +0200, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
> 
> 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.

Other view is that the page is already split therefore nop.

> Make all these functions return -EINVAL to indicate failure instead of
> 0.
> 
> This issue was discovered while experimenting enabling large folios
> without THP and found that returning 0 in these functions is resulting in
> undefined behavior in truncate operations. This change fixes the issue.

Could you elaborate on the undefined behaviour? I don't see it.

If you argue that this code should not be reachable on !THP config, add
WARN() there. But I don't see a value.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov