tipc: switch order of device registration to fix a crash

When tipc is loaded while many processes try to create a TIPC socket,
a crash occurs:
 PANIC: Unable to handle kernel paging request at virtual
 address "dfff20000000021d"
 pc : tipc_sk_create+0x374/0x1180 [tipc]
 lr : tipc_sk_create+0x374/0x1180 [tipc]
   Exception class = DABT (current EL), IL = 32 bits
 Call trace:
  tipc_sk_create+0x374/0x1180 [tipc]
  __sock_create+0x1cc/0x408
  __sys_socket+0xec/0x1f0
  __arm64_sys_socket+0x74/0xa8
 ...

This is due to race between sock_create and unfinished
register_pernet_device. tipc_sk_insert tries to do
"net_generic(net, tipc_net_id)".
but tipc_net_id is not initialized yet.

So switch the order of the two to close the race.

This can be reproduced with multiple processes doing socket(AF_TIPC, ...)
and one process doing module removal.

Fixes: a62fbcc ("tipc: make subscriber server support net namespace")
Signed-off-by: Junwei Hu <hujunwei4@huawei.com>
Reported-by: Wang Wang <wangwang2@huawei.com>
Reviewed-by: Xiaogang Wang <wangxiaogang3@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Junwei Hu

net/tipc/core.c

@@ -131,10 +131,6 @@ static int __init tipc_init(void)
 	if (err)
 		goto out_netlink_compat;
 
-	err = tipc_socket_init();
-	if (err)
-		goto out_socket;
-
 	err = tipc_register_sysctl();
 	if (err)
 		goto out_sysctl;
@@ -143,19 +139,23 @@ static int __init tipc_init(void)
 	if (err)
 		goto out_pernet;
 
+	err = tipc_socket_init();
+	if (err)
+		goto out_socket;
+
 	err = tipc_bearer_setup();
 	if (err)
 		goto out_bearer;
 
 	pr_info("Started in single node mode\n");
 	return 0;
 out_bearer:
+	tipc_socket_stop();
+out_socket:
 	unregister_pernet_subsys(&tipc_net_ops);
 out_pernet:
 	tipc_unregister_sysctl();
 out_sysctl:
-	tipc_socket_stop();
-out_socket:
 	tipc_netlink_compat_stop();
 out_netlink_compat:
 	tipc_netlink_stop();
@@ -167,10 +167,10 @@ static int __init tipc_init(void)
 static void __exit tipc_exit(void)
 {
 	tipc_bearer_cleanup();
+	tipc_socket_stop();
 	unregister_pernet_subsys(&tipc_net_ops);
 	tipc_netlink_stop();
 	tipc_netlink_compat_stop();
-	tipc_socket_stop();
 	tipc_unregister_sysctl();
 
 	pr_info("Deactivated\n");