Merge branch 'xen-netback-synchronization'

Merge branch 'xen-netback-synchronization'

Wei Liu says:

====================
xen-netback: synchronisation between core driver and netback

The zero-copy netback has far more interactions with core network driver than
the old copying backend. One significant thing is that netback now relies on
a callback from core driver to correctly release resources.

However correct synchronisation between core driver and netback is missing.
Currently netback relies on a loop to wait for core driver to release
resources. This is proven not enough and erroneous recently, partly due to code
structure, partly due to missing synchronisation. Short-live domains like
OpenMirage unikernels can easily trigger race in backend, rendering backend
unresponsive.

This patch series aims to slove this issue by introducing proper
synchronisation between core driver and netback.

Chagges in v4:
* avoid using wait queue
* remove dedicated loop for netif_napi_del
* remove unnecessary check on callback

Change in v3: improve commit message in patch 1

Change in v2: fix Zoltan's email address in commit message
====================

Signed-off-by: David S. Miller <davem@davemloft.net>