linux-kernel - Re: [PATCH v2] huge_memory: return -EINVAL in folio split functions when THP is disabled

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Message-ID: <74886543-6038-4444-8E2F-3F3169171837@nvidia.com>
Date: Thu, 04 Sep 2025 09:21:20 -0400
From: Zi Yan <ziy@...dia.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: Ryan Roberts <ryan.roberts@....com>, David Hildenbrand <david@...hat.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>, Barry Song <baohua@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>, Nico Pache <npache@...hat.com>,
 Dev Jain <dev.jain@....com>, "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 linux-kernel@...r.kernel.org, willy@...radead.org, linux-mm@...ck.org,
 mcgrof@...nel.org, gost.dev@...sung.com, Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH v2] huge_memory: return -EINVAL in folio split functions
 when THP is disabled

On 4 Sep 2025, at 5:51, 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. As large folios depend on CONFIG_THP, issue warning as this function
> should not be called without a large folio.
>
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> ---
> 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.
>
>  include/linux/huge_mm.h | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
Acked-by: Zi Yan <ziy@...dia.com>

Best Regards,
Yan, Zi