Re: [Patch v2] mm/huge_memory: fix NULL pointer deference when splitting folio

[Zi Yan <ziy@nvidia.com>]

On 19 Nov 2025, at 18:53, Wei Yang wrote:

> Commit c010d47f107f ("mm: thp: split huge page to any lower order
> pages") introduced an early check on the folio's order via
> mapping->flags before proceeding with the split work.
>
> This check introduced a bug: for shmem folios in the swap cache and
> truncated folios, the mapping pointer can be NULL. Accessing
> mapping->flags in this state leads directly to a NULL pointer
> dereference.
>
> This commit fixes the issue by moving the check for mapping != NULL
> before any attempt to access mapping->flags.
>
> Fixes: c010d47f107f ("mm: thp: split huge page to any lower order pages")
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: "David Hildenbrand (Red Hat)" <david@kernel.org>
> Cc: <stable@vger.kernel.org>
>
> ---
> This patch is based on current mm-new, latest commit:
>
>     febb34c02328 dt-bindings: riscv: Add Svrsw60t59b extension description
>
> v2:
>   * just move folio->mapping ahead
> ---
>  mm/huge_memory.c | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
>

Thanks. Reviewed-by: Zi Yan <ziy@nvidia.com>

Best Regards,
Yan, Zi