Re: [PATCH v3 15/47] mm/khugepaged: always recheck the pmd in try_collapse_pte_mapped_thp()

[Lance Yang]

On Sat, Oct 31, 2026 at 10:39:44AM +0100, David Hildenbrand (Arm) wrote:
>From: Josef Bacik <josef@xxxxxxxxxxxxxx>
>
>try_collapse_pte_mapped_thp() drops the PTE lock after it has cleared the
>page table, and takes the PMD lock and the PTE lock to remove it.
>
>In between, MADV_DONTNEED with CONFIG_PT_RECLAIM can reclaim the
>page table. The pmd_same() check is supposed to handle this, but it is
>only done with CONFIG_SPLIT_PTE_PTLOCKS.
>
>Fix it by performing the check unconditionally.
>
>Fix generated by an LLM and sent by Josef Bacik in private.
>
>Fixes: 6375e95f381e ("mm: pgtable: reclaim empty PTE page in madvise(MADV_DONTNEED)")
>Cc: stable@xxxxxxxxxxxxxxx
>Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
>[ david: adjust description ]
>Reviewed-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
>Tested-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
>Tested-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
>Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
>---

Nothing jumped out at me, so:

Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>