Re: [PATCH 15/46] mm/khugepaged: always recheck the pmd in try_collapse_pte_mapped_thp()

[Gregory Price]

On 2026-10-27 00:17 +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 ]
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Reviewed-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
Tested-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>

-- 
Gregory Price (Meta) <gourry@xxxxxxxxxx>