net/smc: use rcu_barrier() on module unload

Add rcu_barrier() to make sure no RCU readers or callbacks are
pending when the module is unloaded.

Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/smc/af_smc.c

@@ -25,6 +25,7 @@
 #include <linux/in.h>
 #include <linux/sched/signal.h>
 #include <linux/if_vlan.h>
+#include <linux/rcupdate_wait.h>
 
 #include <net/sock.h>
 #include <net/tcp.h>
@@ -2111,6 +2112,7 @@ static void __exit smc_exit(void)
 	proto_unregister(&smc_proto);
 	smc_pnet_exit();
 	unregister_pernet_subsys(&smc_net_ops);
+	rcu_barrier();
 }
 
 module_init(smc_init);