openvswitch: Return vport module ref before destruction

Return module reference before invoking the respective vport
->destroy() function. This is needed as ovs_vport_del() is not
invoked inside an RCU read side critical section so the kfree
can occur immediately before returning to ovs_vport_del().

Returning the module reference before ->destroy() is safe because
the module unregistration is blocked on ovs_lock which we hold
while destroying the datapath.

Fixes: 62b9c8d0 ("ovs: Turn vports with dependencies into separate modules")
Reported-by: NPravin Shelar <pshelar@nicira.com>
Signed-off-by: NThomas Graf <tgraf@suug.ch>
Acked-by: NPravin B Shelar <pshelar@nicira.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/openvswitch/vport.c

@@ -274,10 +274,8 @@ void ovs_vport_del(struct vport *vport)
 	ASSERT_OVSL();
 
 	hlist_del_rcu(&vport->hash_node);
-
-	vport->ops->destroy(vport);
-
 	module_put(vport->ops->owner);
+	vport->ops->destroy(vport);
 }
 
 /**