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

*** 18,28 ****
   *
   * CDDL HEADER END
   */
  /*
   * Copyright (c) 1992, 2010, Oracle and/or its affiliates. All rights reserved.
!  * Copyright 2019 Joyent, Inc.
   */
  
  /*      Copyright (c) 1990, 1991 UNIX System Laboratories, Inc. */
  /*      Copyright (c) 1984, 1986, 1987, 1988, 1989, 1990 AT&T   */
  /*      All Rights Reserved   */
--- 18,28 ----
   *
   * CDDL HEADER END
   */
  /*
   * Copyright (c) 1992, 2010, Oracle and/or its affiliates. All rights reserved.
!  * Copyright 2021 Joyent, Inc.
   */
  
  /*      Copyright (c) 1990, 1991 UNIX System Laboratories, Inc. */
  /*      Copyright (c) 1984, 1986, 1987, 1988, 1989, 1990 AT&T   */
  /*      All Rights Reserved   */
*** 761,771 ****
          ASSERT(removectx(t, NULL, brand_interpositioning_disable,
              brand_interpositioning_enable, NULL, NULL,
              brand_interpositioning_disable, NULL) == 0);
          installctx(t, NULL, brand_interpositioning_disable,
              brand_interpositioning_enable, NULL, NULL,
!             brand_interpositioning_disable, NULL);
  
          if (t == curthread) {
                  kpreempt_disable();
                  brand_interpositioning_enable();
                  kpreempt_enable();
--- 761,771 ----
          ASSERT(removectx(t, NULL, brand_interpositioning_disable,
              brand_interpositioning_enable, NULL, NULL,
              brand_interpositioning_disable, NULL) == 0);
          installctx(t, NULL, brand_interpositioning_disable,
              brand_interpositioning_enable, NULL, NULL,
!             brand_interpositioning_disable, NULL, NULL);
  
          if (t == curthread) {
                  kpreempt_disable();
                  brand_interpositioning_enable();
                  kpreempt_enable();
*** 827,836 ****
--- 827,837 ----
          void (*restop)(klwp_t *) = lwp_getdatamodel(lwp) == DATAMODEL_NATIVE ?
              lwp_segregs_restore : lwp_segregs_restore32;
  #else
          void (*restop)(klwp_t *) = lwp_segregs_restore;
  #endif
+         struct ctxop *ctx;
  
          /*
           * Install the basic lwp context handlers on each lwp.
           *
           * On the amd64 kernel, the context handlers are responsible for
*** 842,855 ****
           * On the i386 kernel, the context handlers are responsible for
           * virtualizing %gs/%fs to the lwp by updating the per-cpu GDTs
           */
          ASSERT(removectx(t, lwp, lwp_segregs_save, restop,
              NULL, NULL, NULL, NULL) == 0);
!         if (thisthread)
                  kpreempt_disable();
          installctx(t, lwp, lwp_segregs_save, restop,
!             NULL, NULL, NULL, NULL);
          if (thisthread) {
                  /*
                   * Since we're the right thread, set the values in the GDT
                   */
                  restop(lwp);
--- 843,860 ----
           * On the i386 kernel, the context handlers are responsible for
           * virtualizing %gs/%fs to the lwp by updating the per-cpu GDTs
           */
          ASSERT(removectx(t, lwp, lwp_segregs_save, restop,
              NULL, NULL, NULL, NULL) == 0);
!         if (thisthread) {
!                 ctx = installctx_preallocate();
                  kpreempt_disable();
+         } else {
+                 ctx = NULL;
+         }
          installctx(t, lwp, lwp_segregs_save, restop,
!             NULL, NULL, NULL, NULL, ctx);
          if (thisthread) {
                  /*
                   * Since we're the right thread, set the values in the GDT
                   */
                  restop(lwp);
*** 872,885 ****
                      SA(sizeof (struct regs) + MINFRAME);
  #endif
                  ASSERT(removectx(t, kstktop,
                      sep_save, sep_restore, NULL, NULL, NULL, NULL) == 0);
  
!                 if (thisthread)
                          kpreempt_disable();
                  installctx(t, kstktop,
!                     sep_save, sep_restore, NULL, NULL, NULL, NULL);
                  if (thisthread) {
                          /*
                           * We're the right thread, so set the stack pointer
                           * for the first sysenter instruction to use
                           */
--- 877,894 ----
                      SA(sizeof (struct regs) + MINFRAME);
  #endif
                  ASSERT(removectx(t, kstktop,
                      sep_save, sep_restore, NULL, NULL, NULL, NULL) == 0);
  
!                 if (thisthread) {
!                         ctx = installctx_preallocate();
                          kpreempt_disable();
+                 } else {
+                         ctx = NULL;
+                 }
                  installctx(t, kstktop,
!                     sep_save, sep_restore, NULL, NULL, NULL, NULL, ctx);
                  if (thisthread) {
                          /*
                           * We're the right thread, so set the stack pointer
                           * for the first sysenter instruction to use
                           */