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

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Message-ID: <6d3faf73-c8aa-db9a-1629-a9de85a1b377@oracle.com>
Date:   Tue, 16 Jan 2018 13:47:01 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Ross Lagerwall <ross.lagerwall@...rix.com>,
        xen-devel@...ts.xenproject.org
Cc:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] xen/grant-table: Use put_page instead of free_page

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@...rix.com>

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