diff --git a/etc/nova/rootwrap.d/compute.filters b/etc/nova/rootwrap.d/compute.filters
index e98c3f265daf..87f3d37624c7 100644
--- a/etc/nova/rootwrap.d/compute.filters
+++ b/etc/nova/rootwrap.d/compute.filters
@@ -31,6 +31,10 @@ qemu-nbd: CommandFilter, qemu-nbd, root
 # nova/virt/disk/mount/loop.py: 'losetup', '--detach', device
 losetup: CommandFilter, losetup, root
 
+# nova/virt/libvirt/utils.py: 'blockdev', '--getsize64', path
+# nova/virt/disk/mount/nbd.py: 'blockdev', '--flushbufs', device
+blockdev: RegExpFilter, blockdev, root, blockdev, (--getsize64|--flushbufs), /dev/.*
+
 # nova/virt/disk/vfs/localfs.py: 'tee', canonpath
 tee: CommandFilter, tee, root
 
diff --git a/nova/tests/virt/test_virt.py b/nova/tests/virt/test_virt.py
index 5048fc7562e7..6fa1a63cc674 100644
--- a/nova/tests/virt/test_virt.py
+++ b/nova/tests/virt/test_virt.py
@@ -125,12 +125,14 @@ class TestVirtDisk(test.NoDBTestCase):
 
         disk_api.teardown_container('/mnt/nbd/nopart')
         expected_commands += [
+                              ('blockdev', '--flushbufs', '/dev/nbd15'),
                               ('umount', '/dev/nbd15'),
                               ('qemu-nbd', '-d', '/dev/nbd15'),
                              ]
 
         disk_api.teardown_container('/mnt/nbd/part')
         expected_commands += [
+                              ('blockdev', '--flushbufs', '/dev/nbd15'),
                               ('umount', '/dev/mapper/nbd15p1'),
                               ('kpartx', '-d', '/dev/nbd15'),
                               ('qemu-nbd', '-d', '/dev/nbd15'),
diff --git a/nova/virt/disk/mount/api.py b/nova/virt/disk/mount/api.py
index fb0ba8d5fe55..6a545b7000d5 100644
--- a/nova/virt/disk/mount/api.py
+++ b/nova/virt/disk/mount/api.py
@@ -205,10 +205,14 @@ class Mount(object):
         """Unmount the device from the file system."""
         if not self.mounted:
             return
+        self.flush_dev()
         LOG.debug(_("Umount %s") % self.mapped_device)
         utils.execute('umount', self.mapped_device, run_as_root=True)
         self.mounted = False
 
+    def flush_dev(self):
+        pass
+
     def do_mount(self):
         """Call the get, map and mnt operations."""
         status = False
diff --git a/nova/virt/disk/mount/nbd.py b/nova/virt/disk/mount/nbd.py
index 801e25eba35c..cc33bc64b448 100644
--- a/nova/virt/disk/mount/nbd.py
+++ b/nova/virt/disk/mount/nbd.py
@@ -129,3 +129,12 @@ class NbdMount(api.Mount):
         utils.execute('qemu-nbd', '-d', self.device, run_as_root=True)
         self.linked = False
         self.device = None
+
+    def flush_dev(self):
+        """flush NBD block device buffer."""
+        # Perform an explicit BLKFLSBUF to support older qemu-nbd(s).
+        # Without this flush, when a nbd device gets re-used the
+        # qemu-nbd intermittently hangs.
+        if self.device:
+            utils.execute('blockdev', '--flushbufs',
+                          self.device, run_as_root=True)