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

[Pankaj Raghav <kernel@pankajraghav.com>]

On 9/2/25 10:43, David Hildenbrand wrote:
> On 02.09.25 10:40, 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.
>>
>> 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.
> 
> Currently large folios that could be split are impossible without THP, so why should this be a fix?
> 
I was debating with myself whether it will classify as a fix or not. I have had people tell me that
I should mention it as fix even though I didn't feel like it ;)

But I agree with you, we can't hit this issue in the upstream kernel. I can remove the fixes tag in
the next version.

--
Pankaj