OS-7753 THREAD_KPRI_RELEASE does nothing of the sort
Reviewed by: Bryan Cantrill <bryan@joyent.com>
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>

*** 19,32 ****
   * CDDL HEADER END
   */
  /*
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
- #pragma ident   "%Z%%M% %I%     %E% SMI"
- 
  #if defined(lint)
  #include <sys/types.h>
  #include <sys/thread.h>
  #include <sys/cpuvar.h>
  #else   /* lint */
--- 19,31 ----
   * CDDL HEADER END
   */
  /*
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
+  * Copyright 2019 Joyent, Inc.
   */
  
  #if defined(lint)
  #include <sys/types.h>
  #include <sys/thread.h>
  #include <sys/cpuvar.h>
  #else   /* lint */
*** 500,513 ****
          .align  16
          ENTRY(rw_enter)
          cmp     %o1, RW_WRITER                  ! entering as writer?
          be,a,pn %icc, 2f                        ! if so, go do it ...
          or      THREAD_REG, RW_WRITE_LOCKED, %o5 ! delay: %o5 = owner
-         ld      [THREAD_REG + T_KPRI_REQ], %o3  ! begin THREAD_KPRI_REQUEST()
          ldn     [%o0], %o4                      ! %o4 = old lock value
-         inc     %o3                             ! bump kpri
-         st      %o3, [THREAD_REG + T_KPRI_REQ]  ! store new kpri
  1:
          andcc   %o4, RW_WRITE_CLAIMED, %g0      ! write-locked or write-wanted?
          bz,pt   %xcc, 3f                        ! if so, prepare to block
          add     %o4, RW_READ_LOCK, %o5          ! delay: increment hold count
          sethi   %hi(rw_enter_sleep), %o2        ! load up jump
--- 499,509 ----
*** 550,568 ****
          membar  #LoadStore|#StoreStore          ! membar_exit()
          subcc   %o4, RW_READ_LOCK, %o5          ! %o5 = new lock value if reader
          bnz,pn  %xcc, 2f                        ! single reader, no waiters?
          clr     %o1
  1:
-         ld      [THREAD_REG + T_KPRI_REQ], %g1  ! begin THREAD_KPRI_RELEASE()
          srl     %o4, RW_HOLD_COUNT_SHIFT, %o3   ! %o3 = hold count (lockstat)
          casx    [%o0], %o4, %o5                 ! try to drop lock
          cmp     %o4, %o5                        ! did we succeed?
          bne,pn  %xcc, rw_exit_wakeup            ! if not, go to C
!         dec     %g1                             ! delay: drop kpri
  .rw_read_exit_lockstat_patch_point:
          retl
!         st      %g1, [THREAD_REG + T_KPRI_REQ]  ! delay: store new kpri
  2:
          andcc   %o4, RW_WRITE_LOCKED, %g0       ! are we a writer?
          bnz,a,pt %xcc, 3f
          or      THREAD_REG, RW_WRITE_LOCKED, %o4 ! delay: %o4 = owner
          cmp     %o5, RW_READ_LOCK               ! would lock still be held?
--- 546,563 ----
          membar  #LoadStore|#StoreStore          ! membar_exit()
          subcc   %o4, RW_READ_LOCK, %o5          ! %o5 = new lock value if reader
          bnz,pn  %xcc, 2f                        ! single reader, no waiters?
          clr     %o1
  1:
          srl     %o4, RW_HOLD_COUNT_SHIFT, %o3   ! %o3 = hold count (lockstat)
          casx    [%o0], %o4, %o5                 ! try to drop lock
          cmp     %o4, %o5                        ! did we succeed?
          bne,pn  %xcc, rw_exit_wakeup            ! if not, go to C
!         nop                                     ! delay: do nothing
  .rw_read_exit_lockstat_patch_point:
          retl
!         nop                                     ! delay: do nothing
  2:
          andcc   %o4, RW_WRITE_LOCKED, %g0       ! are we a writer?
          bnz,a,pt %xcc, 3f
          or      THREAD_REG, RW_WRITE_LOCKED, %o4 ! delay: %o4 = owner
          cmp     %o5, RW_READ_LOCK               ! would lock still be held?