Function sock_register() returns a negative integer on failure. In function caif_sktinit_module() defined in net/caif/caif_socket.c, the return value of sock_register() is checked. However, no matter whether the return value of sock_register() is zero, it will returns 0 (indicates success). I guess the symbol not "!" is a typo in the check statement at line 1111. Codes related to this bug are shown as below.

caif_sktinit_module @@ net/caif/caif_socket.c
1108 static int __init caif_sktinit_module(void)
1109 {
1110     int err = sock_register(&caif_family_ops);
1111     if (!err)     // use if(err) ?
1112         return err;
1113     return 0;
1114 }

Thanks very much!