RDS/IB: wait for IB dev freeing work to finish during rmmod

The RDS IB client removal callback can queue work to drop the final reference
to an IB device.  We have to make sure that this function has returned before
we complete rmmod or the work threads can try to execute freed code.
Signed-off-by: NZach Brown <zach.brown@oracle.com>

net/rds/ib.c

@@ -336,11 +336,18 @@ static int rds_ib_laddr_check(__be32 addr)
 	return ret;
 }
 
+static void rds_ib_unregister_client(void)
+{
+	ib_unregister_client(&rds_ib_client);
+	/* wait for rds_ib_dev_free() to complete */
+	flush_workqueue(rds_wq);
+}
+
 void rds_ib_exit(void)
 {
 	rds_info_deregister_func(RDS_INFO_IB_CONNECTIONS, rds_ib_ic_info);
 	rds_ib_destroy_nodev_conns();
-	ib_unregister_client(&rds_ib_client);
+	rds_ib_unregister_client();
 	rds_ib_sysctl_exit();
 	rds_ib_recv_exit();
 	rds_trans_unregister(&rds_ib_transport);
@@ -404,7 +411,7 @@ int __init rds_ib_init(void)
 out_sysctl:
 	rds_ib_sysctl_exit();
 out_ibreg:
-	ib_unregister_client(&rds_ib_client);
+	rds_ib_unregister_client();
 out:
 	return ret;
 }