12976 system panics with error in IP module
Reviewed by: Andy Fiddaman <andy@omniosce.org>
Reviewed by: Paul Winder <p.winder@me.com>

*** 19,28 ****
--- 19,29 ----
   * CDDL HEADER END
   */
  /*
   * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright 2019 OmniOS Community Edition (OmniOSce) Association.
+  * Copyright 2020 Joyent, Inc.
   */
  
  #ifndef _SYS_SOCKET_PROTO_H_
  #define _SYS_SOCKET_PROTO_H_
  
*** 200,210 ****
--- 201,220 ----
                      struct sock_proto_props *);
          void    (*su_txq_full)(sock_upper_handle_t, boolean_t);
          void    (*su_signal_oob)(sock_upper_handle_t, ssize_t);
          void    (*su_zcopy_notify)(sock_upper_handle_t);
          void    (*su_set_error)(sock_upper_handle_t, int);
+         /*
+          * NOTE: This function frees upper handle items. Caller cannot
+          * rely on them after this upcall.
+          */
          void    (*su_closed)(sock_upper_handle_t);
+         /*
+          * NOTE: This function MUST be implemented without using lower-level
+          * downcalls or accesses. This allows callers to ensure su_closed()
+          * upcalls can happen indepdently or concurrently.
+          */
          vnode_t *(*su_get_vnode)(sock_upper_handle_t);
  };
  
  #define SOCK_UC_VERSION         sizeof (sock_upcalls_t)
  #define SOCK_DC_VERSION         sizeof (sock_downcalls_t)