OS-4144 panic in lx_freelwp during zone shutdown
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>

*** 25,35 ****
  
  /*      Copyright (c) 1988 AT&T */
  /*        All Rights Reserved   */
  
  /*
!  * Copyright (c) 2013, Joyent, Inc. All rights reserved.
   */
  
  #include <sys/types.h>
  #include <sys/param.h>
  #include <sys/sysmacros.h>
--- 25,35 ----
  
  /*      Copyright (c) 1988 AT&T */
  /*        All Rights Reserved   */
  
  /*
!  * Copyright 2015, Joyent, Inc.
   */
  
  #include <sys/types.h>
  #include <sys/param.h>
  #include <sys/sysmacros.h>
*** 155,165 ****
          boolean_t in_arg;
          int argc = 0;
          int error = 0, count = 0;
          proc_t *p = ttoproc(curthread);
          klwp_t *lwp = ttolwp(curthread);
!         int brand_action;
  
          if (args == NULL)
                  args = "";
  
          alen = strlen(initpath) + 1 + strlen(args) + 1;
--- 155,165 ----
          boolean_t in_arg;
          int argc = 0;
          int error = 0, count = 0;
          proc_t *p = ttoproc(curthread);
          klwp_t *lwp = ttolwp(curthread);
!         int brand_action = EBA_NONE;
  
          if (args == NULL)
                  args = "";
  
          alen = strlen(initpath) + 1 + strlen(args) + 1;
*** 266,276 ****
           * parent process's signal mask.  Clear it now so that we behave in
           * the same way as when started from the global zone.
           */
          sigemptyset(&curthread->t_hold);
  
!         brand_action = ZONE_IS_BRANDED(p->p_zone) ? EBA_BRAND : EBA_NONE;
  again:
          error = exec_common((const char *)(uintptr_t)exec_fnamep,
              (const char **)(uintptr_t)uap, NULL, brand_action);
  
          /*
--- 266,284 ----
           * parent process's signal mask.  Clear it now so that we behave in
           * the same way as when started from the global zone.
           */
          sigemptyset(&curthread->t_hold);
  
!         /*
!          * Only instruct exec_common to brand the process if necessary.  It is
!          * possible that the init process is already properly branded due to the
!          * proc_exit -> restart_init -> exec_init call chain.
!          */
!         if (ZONE_IS_BRANDED(p->p_zone) &&
!             p->p_brand != p->p_zone->zone_brand) {
!                 brand_action = EBA_BRAND;
!         }
  again:
          error = exec_common((const char *)(uintptr_t)exec_fnamep,
              (const char **)(uintptr_t)uap, NULL, brand_action);
  
          /*