From 745282256c754ac5ed3dbe2fbef6471dc1373417 Mon Sep 17 00:00:00 2001
From: Jennifer Herbert <jennifer.herbert@citrix.com>
Date: Mon, 5 Jan 2015 15:07:46 +0000
Subject: [PATCH] xen/gntdev: safely unmap grants in case they are still in use

Use gnttab_unmap_refs_async() to wait until the mapped pages are no
longer in use before unmapping them.

This allows userspace programs to safely use Direct I/O and AIO to a
network filesystem which may retain refs to pages in queued skbs after
the filesystem I/O has completed.

Signed-off-by: Jennifer Herbert <jennifer.herbert@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
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