OS-6441 netstack_find_by_stackid() drops-and-reacquires

*** 121,130 ****
--- 121,131 ----
  static boolean_t netstack_apply_destroy(kmutex_t *, netstack_t *, int);
  static boolean_t wait_for_zone_creator(netstack_t *, kmutex_t *);
  static boolean_t wait_for_nms_inprogress(netstack_t *, nm_state_t *,
      kmutex_t *);
  
+ static void netstack_hold_locked(netstack_t *);
  static void netstack_reap_work(netstack_t *, boolean_t);
  ksema_t netstack_reap_limiter;
  
  void
  netstack_init(void)
*** 1035,1046 ****
          mutex_enter(&netstack_g_lock);
          for (ns = netstack_head; ns != NULL; ns = ns->netstack_next) {
                  mutex_enter(&ns->netstack_lock);
                  if (ns->netstack_stackid == stackid &&
                      !(ns->netstack_flags & (NSF_UNINIT|NSF_CLOSING))) {
                          mutex_exit(&ns->netstack_lock);
-                         netstack_hold(ns);
                          mutex_exit(&netstack_g_lock);
                          return (ns);
                  }
                  mutex_exit(&ns->netstack_lock);
          }
--- 1036,1047 ----
          mutex_enter(&netstack_g_lock);
          for (ns = netstack_head; ns != NULL; ns = ns->netstack_next) {
                  mutex_enter(&ns->netstack_lock);
                  if (ns->netstack_stackid == stackid &&
                      !(ns->netstack_flags & (NSF_UNINIT|NSF_CLOSING))) {
+                         netstack_hold_locked(ns);
                          mutex_exit(&ns->netstack_lock);
                          mutex_exit(&netstack_g_lock);
                          return (ns);
                  }
                  mutex_exit(&ns->netstack_lock);
          }
*** 1193,1210 ****
                          netstack_reap_work(ns, is_not_intr);
                  }
          }
  }
  
  void
  netstack_hold(netstack_t *ns)
  {
          mutex_enter(&ns->netstack_lock);
!         ns->netstack_refcnt++;
!         ASSERT(ns->netstack_refcnt > 0);
          mutex_exit(&ns->netstack_lock);
-         DTRACE_PROBE1(netstack__inc__ref, netstack_t *, ns);
  }
  
  /*
   * To support kstat_create_netstack() using kstat_zone_add we need
   * to track both
--- 1194,1218 ----
                          netstack_reap_work(ns, is_not_intr);
                  }
          }
  }
  
+ static void
+ netstack_hold_locked(netstack_t *ns)
+ {
+         ASSERT(MUTEX_HELD(&ns->netstack_lock));
+         ns->netstack_refcnt++;
+         ASSERT(ns->netstack_refcnt > 0);
+         DTRACE_PROBE1(netstack__inc__ref, netstack_t *, ns);
+ }
+ 
  void
  netstack_hold(netstack_t *ns)
  {
          mutex_enter(&ns->netstack_lock);
!         netstack_hold_locked(ns);
          mutex_exit(&ns->netstack_lock);
  }
  
  /*
   * To support kstat_create_netstack() using kstat_zone_add we need
   * to track both