Re: [PATCH 1/2] xen/grant-table: Use put_page instead of free_page

[Boris Ostrovsky]

On 01/11/2018 04:36 AM, Ross Lagerwall wrote:
> The page given to gnttab_end_foreign_access() to free could be a
> compound page so use put_page() instead of free_page() since it can
> handle both compound and single pages correctly.
>
> This bug was discovered when migrating a Xen VM with several VIFs and
> CONFIG_DEBUG_VM enabled. It hits a BUG usually after fewer than 10
> iterations. All netfront devices disconnect from the backend during a
> suspend/resume and this will call gnttab_end_foreign_access() if a
> netfront queue has an outstanding skb. The mismatch between calling
> get_page() and free_page() on a compound page causes a reference
> counting error which is detected when DEBUG_VM is enabled.
>
> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>