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

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Message-ID: <1acb705c-4846-4a12-9e90-f7853da8a295@redhat.com>
Date: Tue, 2 Sep 2025 10:43:19 +0200
From: David Hildenbrand <david@...hat.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
 Ryan Roberts <ryan.roberts@....com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
 Nico Pache <npache@...hat.com>, Zi Yan <ziy@...dia.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, willy@...radead.org,
 mcgrof@...nel.org, gost.dev@...sung.com, Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH] huge_memory: return -EINVAL in folio split functions when
 THP is disabled

On 02.09.25 10:40, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@...sung.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?

-- 
Cheers

David / dhildenb