Fix for 13717 may break 8-disk raidz2

*** 1379,1392 ****
           * We might have already saved once (due to a prior use of the kernel
           * FPU or another code path) so FPU_VALID could be set. This is handled
           * by fp_save, as is the FPU_EN check.
           */
          if (pl != NULL) {
                  kpreempt_disable();
!                 if ((flags & KFPU_USE_LWP) == 0)
!                         fp_save(&pl->lwp_pcb.pcb_fpu);
!                 pl->lwp_pcb.pcb_fpu.fpu_flags |= FPU_KERNEL;
                  kpreempt_enable();
          }
  
          /*
           * Set the context operations for kernel FPU usage. Note that this
--- 1379,1409 ----
           * We might have already saved once (due to a prior use of the kernel
           * FPU or another code path) so FPU_VALID could be set. This is handled
           * by fp_save, as is the FPU_EN check.
           */
          if (pl != NULL) {
+                 fpu_ctx_t *pf = &pl->lwp_pcb.pcb_fpu;
+ 
                  kpreempt_disable();
!                 if ((flags & KFPU_USE_LWP) == 0) {
!                         fp_save(pf);
!                 } else {
!                         /*
!                          * For pure kernel threads with an LWP, we can use the
!                          * LWP's pcb_fpu to save/restore context.
!                          */
!                         VERIFY(curthread->t_procp->p_flag & SSYS);
!                         VERIFY(kfpu == NULL);
!                         ASSERT((pf->fpu_flags & FPU_EN) == 0);
! 
!                         /* Always restore the fpu to the initial state. */
!                         if (fp_save_mech == FP_XSAVE)
!                                 pf->fpu_xsave_mask = XFEATURE_FP_ALL;
!                         fpinit();
!                         pf->fpu_flags = FPU_EN;
!                 }
!                 pf->fpu_flags |= FPU_KERNEL;
                  kpreempt_enable();
          }
  
          /*
           * Set the context operations for kernel FPU usage. Note that this
*** 1398,1424 ****
          installctx(curthread, kfpu, kernel_fpu_ctx_save, kernel_fpu_ctx_restore,
              NULL, NULL, NULL, NULL);
  
          curthread->t_flag |= T_KFPU;
  
!         if ((flags & KFPU_USE_LWP) == KFPU_USE_LWP) {
!                 /*
!                  * For pure kernel threads with an LWP, we can use the LWP's
!                  * pcb_fpu to save/restore context.
!                  */
!                 fpu_ctx_t *pf = &pl->lwp_pcb.pcb_fpu;
! 
!                 VERIFY(curthread->t_procp->p_flag & SSYS);
!                 VERIFY(kfpu == NULL);
!                 ASSERT((pf->fpu_flags & FPU_EN) == 0);
! 
!                 /* Always restore the fpu to the initial state. */
!                 if (fp_save_mech == FP_XSAVE)
!                         pf->fpu_xsave_mask = XFEATURE_FP_ALL;
!                 fpinit();
!                 pf->fpu_flags = FPU_EN | FPU_KERNEL;
!         } else {
                  /* initialize the kfpu state */
                  kernel_fpu_ctx_restore(kfpu);
          }
  }
  
--- 1415,1425 ----
          installctx(curthread, kfpu, kernel_fpu_ctx_save, kernel_fpu_ctx_restore,
              NULL, NULL, NULL, NULL);
  
          curthread->t_flag |= T_KFPU;
  
!         if ((flags & KFPU_USE_LWP) == 0) {
                  /* initialize the kfpu state */
                  kernel_fpu_ctx_restore(kfpu);
          }
  }