Experimental patch to speed up network namespace destruction under high concurrency load

net_namespace-mutex.patch

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 1fe58167d39a6fb907be443765693e328a1e6b7e..506e6d32fda4ae5071fec1ea397117d161982cb4
100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -426,7 +426,9 @@ static void cleanup_net(struct work_struct *work)
         * This needs to be before calling the exit() notifiers, so
         * the rcu_barrier() below isn't sufficient alone.
         */
+       mutex_unlock(&net_mutex);
        synchronize_rcu();
+       mutex_lock(&net_mutex);

        /* Run all of the network namespace exit methods */
        list_for_each_entry_reverse(ops, &pernet_list, list)