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) 2003, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright 2019 OmniOS Community Edition (OmniOSce) Association.
+  * Copyright 2020 Joyent, Inc.
   */
  
  /*
   * IP PACKET CLASSIFIER
   *
*** 2743,2753 ****
          if ((connp->conn_state_flags & CONN_CLOSING)) {
                  mutex_exit(&connp->conn_lock);
                  return (NULL);
          }
  
!         mutex_exit(&connp->conn_lock);
  
          if (connp->conn_upper_handle != NULL) {
                  vn = (*connp->conn_upcalls->su_get_vnode)
                      (connp->conn_upper_handle);
          } else if (!IPCL_IS_NONSTR(connp) && connp->conn_rq != NULL) {
--- 2744,2758 ----
          if ((connp->conn_state_flags & CONN_CLOSING)) {
                  mutex_exit(&connp->conn_lock);
                  return (NULL);
          }
  
!         /*
!          * Continue to hold conn_lock because we don't want to race with an
!          * in-progress close, which will have set-to-NULL (and destroyed
!          * upper_handle, aka sonode (and vnode)) BEFORE setting CONN_CLOSING.
!          */
  
          if (connp->conn_upper_handle != NULL) {
                  vn = (*connp->conn_upcalls->su_get_vnode)
                      (connp->conn_upper_handle);
          } else if (!IPCL_IS_NONSTR(connp) && connp->conn_rq != NULL) {
*** 2755,2764 ****
--- 2760,2771 ----
                  if (vn != NULL)
                          VN_HOLD(vn);
                  flags |= MIB2_SOCKINFO_STREAM;
          }
  
+         mutex_exit(&connp->conn_lock);
+ 
          if (vn == NULL || VOP_GETATTR(vn, &attr, 0, CRED(), NULL) != 0) {
                  if (vn != NULL)
                          VN_RELE(vn);
                  return (NULL);
          }