Re: [PATCH 13/46] mm/huge_memory: fix truncate racing with PMD zapping

[Pedro Falcato]

On Tue, Oct 27, 2026 at 12:17:33AM +0100, David Hildenbrand (Arm) wrote:
> From: Chris Mason <mason@xxxxxxxxxx>
> 
> zap_huge_pmd_folio() removes the rmap before calling folio_mark_dirty().
> If this was the last mapping, truncation can skip unmapping the folio
> and proceed without waiting for the PMD lock, racing with dirtying.
> 
> ifs_set_range_dirty() can oops if MADV_DONTNEED races with
> ftruncate() on XFS, when we get the folio set dirty after it was found
> to not be mapped anymore.
> 
> Move folio_mark_dirty() and folio_mark_accessed() before rmap removal,
> matching the PTE zap path. This keeps the folio mapped while updating
> its state, so truncation must wait for the page table lock.
> 
> Fix generated by an LLM and sent by Chris Mason in private.
> 
> Fixes: fe6cf984939d ("mm/huge_memory: transfer the pmd dirty bit to the folio on zap")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Chris Mason <mason@xxxxxxxxxx>
> [ david: simplify comment and description ]
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Reviewed-by: Pedro Falcato <pfalcato@xxxxxxx>

-- 
Pedro