dpif-netdev: Hold global port mutex while calling offload API.

We changed datapath port lookup to netdev-offload API usage, but
forgot that port mutex was there not only to protect datapath
port hash map.  It was there also as a workaround solution for
complete unsafety of netdev-offload-dpdk functions.

Turning it back to fix the behaviour and adding a comment to prevent
removing it in the future unless netdev-offload-dpdk fixed.

For the thread safety notice see the top of netdev-offload-dpdk.c.

Fixes: 3011580 ("dpif-netdev: Use netdev-offload API for port lookup while offloading")
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: Eli Britstein <elibr@mellanox.com>

lib/dpif-netdev.c

@@ -2271,7 +2271,11 @@ mark_to_flow_disassociate(struct dp_netdev_pmd_thread *pmd,
 
         port = netdev_ports_get(in_port, pmd->dp->class);
         if (port) {
+            /* Taking a global 'port_mutex' to fulfill thread safety
+             * restrictions for the netdev-offload-dpdk module. */
+            ovs_mutex_lock(&pmd->dp->port_mutex);
             ret = netdev_flow_del(port, &flow->mega_ufid, NULL);
+            ovs_mutex_unlock(&pmd->dp->port_mutex);
             netdev_close(port);
         }
 
@@ -2415,10 +2419,14 @@ dp_netdev_flow_offload_put(struct dp_flow_offload_item *offload)
         netdev_close(port);
         goto err_free;
     }
+    /* Taking a global 'port_mutex' to fulfill thread safety restrictions for
+     * the netdev-offload-dpdk module. */
+    ovs_mutex_lock(&pmd->dp->port_mutex);
     ret = netdev_flow_put(port, &offload->match,
                           CONST_CAST(struct nlattr *, offload->actions),
                           offload->actions_len, &flow->mega_ufid, &info,
                           NULL);
+    ovs_mutex_unlock(&pmd->dp->port_mutex);
     netdev_close(port);
 
     if (ret) {