11909 THREAD_KPRI_RELEASE does nothing of the sort
Reviewed by: Bryan Cantrill <bryan@joyent.com>
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>

*** 22,32 ****
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
  /*
!  * Copyright (c) 2013, Joyent, Inc.  All rights reserved.
   */
  
  #include <sys/param.h>
  #include <sys/thread.h>
  #include <sys/cmn_err.h>
--- 22,32 ----
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
  /*
!  * Copyright 2019 Joyent, Inc.
   */
  
  #include <sys/param.h>
  #include <sys/thread.h>
  #include <sys/cmn_err.h>
*** 267,279 ****
  void (*rw_lock_delay)(uint_t) = NULL;
  
  /*
   * Full-service implementation of rw_enter() to handle all the hard cases.
   * Called from the assembly version if anything complicated is going on.
-  * The only semantic difference between calling rw_enter() and calling
-  * rw_enter_sleep() directly is that we assume the caller has already done
-  * a THREAD_KPRI_REQUEST() in the RW_READER cases.
   */
  void
  rw_enter_sleep(rwlock_impl_t *lp, krw_t rw)
  {
          uintptr_t old, new, lock_value, lock_busy, lock_wait;
--- 267,276 ----
*** 340,358 ****
                          turnstile_exit(lp);
                          continue;
                  }
  
                  /*
!                  * We really are going to block.  Bump the stats, and drop
!                  * kpri if we're a reader.
                   */
                  ASSERT(lp->rw_wwwh & lock_wait);
                  ASSERT(lp->rw_wwwh & RW_LOCKED);
  
                  sleep_time = -gethrtime();
                  if (rw != RW_WRITER) {
-                         THREAD_KPRI_RELEASE();
                          CPU_STATS_ADDQ(CPU, sys, rw_rdfails, 1);
                          (void) turnstile_block(ts, TS_READER_Q, lp,
                              &rw_sobj_ops, NULL, NULL);
                  } else {
                          CPU_STATS_ADDQ(CPU, sys, rw_wrfails, 1);
--- 337,353 ----
                          turnstile_exit(lp);
                          continue;
                  }
  
                  /*
!                  * We really are going to block, so bump the stats.
                   */
                  ASSERT(lp->rw_wwwh & lock_wait);
                  ASSERT(lp->rw_wwwh & RW_LOCKED);
  
                  sleep_time = -gethrtime();
                  if (rw != RW_WRITER) {
                          CPU_STATS_ADDQ(CPU, sys, rw_rdfails, 1);
                          (void) turnstile_block(ts, TS_READER_Q, lp,
                              &rw_sobj_ops, NULL, NULL);
                  } else {
                          CPU_STATS_ADDQ(CPU, sys, rw_wrfails, 1);
*** 364,375 ****
                  LOCKSTAT_RECORD4(LS_RW_ENTER_BLOCK, lp, sleep_time, rw,
                      (old & RW_WRITE_LOCKED) ? 1 : 0,
                      old >> RW_HOLD_COUNT_SHIFT);
  
                  /*
!                  * We wake up holding the lock (and having kpri if we're
!                  * a reader) via direct handoff from the previous owner.
                   */
                  break;
          }
  
          ASSERT(rw_locked(lp, rw));
--- 359,370 ----
                  LOCKSTAT_RECORD4(LS_RW_ENTER_BLOCK, lp, sleep_time, rw,
                      (old & RW_WRITE_LOCKED) ? 1 : 0,
                      old >> RW_HOLD_COUNT_SHIFT);
  
                  /*
!                  * We wake up holding the lock via direct handoff from the
!                  * previous owner.
                   */
                  break;
          }
  
          ASSERT(rw_locked(lp, rw));
*** 392,402 ****
          int count = 0;
  
          while (next_reader != NULL) {
                  if (DISP_PRIO(next_reader) < wpri)
                          break;
-                 next_reader->t_kpri_req++;
                  next_reader = next_reader->t_link;
                  count++;
          }
          return (count);
  }
--- 387,396 ----
*** 521,531 ****
                  }
                  break;
          }
  
          if (lock_value == RW_READ_LOCK) {
-                 THREAD_KPRI_RELEASE();
                  LOCKSTAT_RECORD(LS_RW_EXIT_RELEASE, lp, RW_READER);
          } else {
                  LOCKSTAT_RECORD(LS_RW_EXIT_RELEASE, lp, RW_WRITER);
          }
  }
--- 515,524 ----
*** 537,551 ****
          uintptr_t old;
  
          if (rw != RW_WRITER) {
                  uint_t backoff = 0;
                  int loop_count = 0;
-                 THREAD_KPRI_REQUEST();
                  for (;;) {
                          if ((old = lp->rw_wwwh) & (rw == RW_READER ?
                              RW_WRITE_CLAIMED : RW_WRITE_LOCKED)) {
-                                 THREAD_KPRI_RELEASE();
                                  return (0);
                          }
                          if (casip(&lp->rw_wwwh, old, old + RW_READ_LOCK) == old)
                                  break;
                          if (rw_lock_delay != NULL) {
--- 530,542 ----
*** 571,581 ****
  void
  rw_downgrade(krwlock_t *rwlp)
  {
          rwlock_impl_t *lp = (rwlock_impl_t *)rwlp;
  
-         THREAD_KPRI_REQUEST();
          membar_exit();
  
          if ((lp->rw_wwwh & RW_OWNER) != (uintptr_t)curthread) {
                  rw_panic("rw_downgrade: not owner", lp);
                  return;
--- 562,571 ----
*** 610,620 ****
                          return (0);
                  new = old + RW_WRITE_LOCK(curthread) - RW_READ_LOCK;
          } while (casip(&lp->rw_wwwh, old, new) != old);
  
          membar_enter();
-         THREAD_KPRI_RELEASE();
          LOCKSTAT_RECORD0(LS_RW_TRYUPGRADE_UPGRADE, lp);
          ASSERT(rw_locked(lp, RW_WRITER));
          return (1);
  }
  
--- 600,609 ----