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 <[e-mail]>
Signed-off-by: Karsten Graul <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/smc/af_smc.c

···
 #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>
···
 	proto_unregister(&smc_proto);
 	smc_pnet_exit();
 	unregister_pernet_subsys(&smc_net_ops);
+	rcu_barrier();
 }
 
 module_init(smc_init);