Side-port of OS-2943 zone stuck 'down': references still extant (illumos-joyent 4cb09b44b4f851905a0e8cccbd9bfc834acc2041)

*** 8,18 ****
   * source.  A copy of the CDDL is also available via the Internet at
   * http://www.illumos.org/license/CDDL.
   */
  
  /*
!  * Copyright 2013, Joyent, Inc. All rights reserved.
   */
  
  /*
   * The ZFS/Zone I/O throttle and scheduler attempts to ensure fair access to
   * ZFS I/O resources for each zone.
--- 8,18 ----
   * source.  A copy of the CDDL is also available via the Internet at
   * http://www.illumos.org/license/CDDL.
   */
  
  /*
!  * Copyright 2014, Joyent, Inc. All rights reserved.
   */
  
  /*
   * The ZFS/Zone I/O throttle and scheduler attempts to ensure fair access to
   * ZFS I/O resources for each zone.
*** 1139,1152 ****
          hrtime_t now, unow, udelta;
  
          if (zp->io_type == ZIO_TYPE_IOCTL)
                  return;
  
!         if ((zonep = zone_find_by_id(zp->io_zoneid)) == NULL)
                  return;
  
!         if (zp->io_dispatched == 0)
                  return;
  
          now = gethrtime();
          unow = NANO_TO_MICRO(now);
          udelta = unow - NANO_TO_MICRO(zp->io_dispatched);
--- 1139,1152 ----
          hrtime_t now, unow, udelta;
  
          if (zp->io_type == ZIO_TYPE_IOCTL)
                  return;
  
!         if (zp->io_dispatched == 0)
                  return;
  
!         if ((zonep = zone_find_by_id(zp->io_zoneid)) == NULL)
                  return;
  
          now = gethrtime();
          unow = NANO_TO_MICRO(now);
          udelta = unow - NANO_TO_MICRO(zp->io_dispatched);