Re: [PATCH v2] mm/migrate_device: Clear stale mapping after freeing swapcache

["Zi Yan" <ziy@nvidia.com>]

On Fri Jul 24, 2026 at 4:27 AM EDT, Arvind Yadav wrote:
> __migrate_device_pages() reads the folio mapping before calling
> folio_free_swap(). When folio_free_swap() succeeds, the folio is removed
> from the swap cache, but the saved mapping still points to swap_space.
>
> Passing the stale mapping to folio_migrate_mapping() makes it take the
> mapped-folio path after the swapcache reference has been dropped. This can
> cause an invalid swap_space lock access followed by a folio reference
> count BUG.
>
> Refresh the saved mapping after folio_free_swap() so the current folio
> state is used during migration.
>
> v2:
> - Refresh the mapping using folio_mapping(), as suggested by Zi Yan.
>
> Fixes: df263d9a7dff ("mm/migrate_device: try to handle swapcache pages")
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@kernel.org>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Rakie Kim <rakie.kim@sk.com>
> Cc: Byungchul Park <byungchul@sk.com>
> Cc: Gregory Price <gourry@gourry.net>
> Cc: Ying Huang <ying.huang@linux.alibaba.com>
> Cc: Alistair Popple <apopple@nvidia.com>
> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
> ---
>  mm/migrate_device.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
LGTM. Thanks.

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

-- 
Best Regards,
Yan, Zi