Re: [PATCH v2] mm/vmscan: fix unintended mtc->nmask mutation in alloc_demote_folio()

[David Hildenbrand (Arm)]

On 3/3/26 06:25, Bing Jiao wrote:
> In alloc_demote_folio(), mtc->nmask is set to NULL for the first
> allocation. If that succeeds, it returns without restoring mtc->nmask
> to allowed_mask. For subsequent allocations from the migrate_pages()
> batch, mtc->nmask will be NULL. If the target node then becomes full,
> the fallback allocation will use nmask = NULL, allocating from any
> node allowed by the task cpuset, which for kswapd is all nodes.
> 
> To address this issue, use a local copy of the mtc structure with
> nmask = NULL for the first allocation attempt specifically, ensuring
> the original mtc remains unmodified.
> 
> Fixes: 320080272892 ("mm/demotion: demote pages according to allocation fallback order")
> Signed-off-by: Bing Jiao <bingjiao@xxxxxxxxxx>
> ---
>  mm/vmscan.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David