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

[David Hildenbrand <david@redhat.com>]

On 02.09.25 10:59, Pankaj Raghav wrote:
> 
> 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.

No need to resend, I think Andrew can just drop the comment.

I'll not that I assume with any large folio support (except unsplittable 
things like hugetlb), we would require splitting support.

So calling these functions would rather indicate a bug I think.

Fine with making them return -EINVAL.

With the Fixes: tag dropped

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers

David / dhildenb