13902 Fix for 13717 may break 8-disk raidz2
13915 installctx() blocking allocate causes problems
Portions contributed by: Jerry Jelinek <gjelinek@gmail.com>
Change-Id: I934d69946cec42630fc541fa8c7385b862b69ca2

*** 20,30 ****
   */
  
  /*
   * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
!  * Copyright 2016 Joyent, Inc.
   */
  
  #include <sys/types.h>
  #include <sys/systm.h>
  #include <sys/schedctl.h>
--- 20,30 ----
   */
  
  /*
   * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
!  * Copyright 2021 Joyent, Inc.
   */
  
  #include <sys/types.h>
  #include <sys/systm.h>
  #include <sys/schedctl.h>
*** 111,121 ****
                  if ((error = schedctl_shared_alloc(&ssp, &uaddr)) != 0)
                          return ((caddr_t)(uintptr_t)set_errno(error));
                  bzero(ssp, sizeof (*ssp));
  
                  installctx(t, ssp, schedctl_save, schedctl_restore,
!                     schedctl_fork, NULL, NULL, NULL);
  
                  thread_lock(t); /* protect against ts_tick and ts_update */
                  t->t_schedctl = ssp;
                  t->t_sc_uaddr = uaddr;
                  ssp->sc_cid = t->t_cid;
--- 111,121 ----
                  if ((error = schedctl_shared_alloc(&ssp, &uaddr)) != 0)
                          return ((caddr_t)(uintptr_t)set_errno(error));
                  bzero(ssp, sizeof (*ssp));
  
                  installctx(t, ssp, schedctl_save, schedctl_restore,
!                     schedctl_fork, NULL, NULL, NULL, NULL);
  
                  thread_lock(t); /* protect against ts_tick and ts_update */
                  t->t_schedctl = ssp;
                  t->t_sc_uaddr = uaddr;
                  ssp->sc_cid = t->t_cid;