dpif-netdev: Enter quiescent state after each offloading operation.

If the offloading queue is big and filled continuously, offloading
thread may have no chance to quiesce blocking rcu callbacks and
other threads waiting for synchronization.

Fix that by entering momentary quiescent state after each operation
since we're not holding any rcu-protected memory here.

Fixes: 02bb282 ("dpif-netdev: do hw flow offload in a thread")
Reported-by: Eli Britstein <[email protected]>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2020-February/049768.html
Acked-by: Eli Britstein <[email protected]>
Signed-off-by: Ilya Maximets <[email protected]>

lib/dpif-netdev.c

@@ -2512,6 +2512,7 @@ dp_netdev_flow_offload_main(void *data OVS_UNUSED)
         VLOG_DBG("%s to %s netdev flow\n",
                  ret == 0 ? "succeed" : "failed", op);
         dp_netdev_free_flow_offload(offload);
+        ovsrcu_quiesce();
     }
 
     return NULL;