11679 vn_rele() and friends should VERIFY after mutex
Reviewed by: Dan McDonald <danmcd@joyent.com>

*** 20,29 ****
--- 20,30 ----
   */
  
  /*
   * Copyright (c) 1988, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright 2020 Joyent, Inc.
+  * Copyright 2022 Spencer Evans-Cole.
   * Copyright 2016 Nexenta Systems, Inc.  All rights reserved.
   * Copyright (c) 2011, 2017 by Delphix. All rights reserved.
   * Copyright 2021 OmniOS Community Edition (OmniOSce) Association.
   */
  
*** 840,874 ****
   * on a vnode.
   */
  void
  vn_rele(vnode_t *vp)
  {
-         VERIFY(vp->v_count > 0);
          mutex_enter(&vp->v_lock);
          if (vp->v_count == 1) {
                  mutex_exit(&vp->v_lock);
                  VOP_INACTIVE(vp, CRED(), NULL);
                  return;
          }
          VN_RELE_LOCKED(vp);
          mutex_exit(&vp->v_lock);
  }
  
  void
  vn_phantom_rele(vnode_t *vp)
  {
-         VERIFY(vp->v_count > 0);
- 
          mutex_enter(&vp->v_lock);
          VERIFY3U(vp->v_count, >=, vp->v_phantom_count);
          vp->v_phantom_count--;
          DTRACE_PROBE1(vn__phantom_rele, vnode_t *, vp);
          if (vp->v_count == 1) {
                  ASSERT0(vp->v_phantom_count);
                  mutex_exit(&vp->v_lock);
                  VOP_INACTIVE(vp, CRED(), NULL);
                  return;
          }
          VN_RELE_LOCKED(vp);
          mutex_exit(&vp->v_lock);
  }
  
--- 841,876 ----
   * on a vnode.
   */
  void
  vn_rele(vnode_t *vp)
  {
          mutex_enter(&vp->v_lock);
          if (vp->v_count == 1) {
                  mutex_exit(&vp->v_lock);
                  VOP_INACTIVE(vp, CRED(), NULL);
                  return;
+         } else {
+                 VERIFY(vp->v_count > 0);
          }
          VN_RELE_LOCKED(vp);
          mutex_exit(&vp->v_lock);
  }
  
  void
  vn_phantom_rele(vnode_t *vp)
  {
          mutex_enter(&vp->v_lock);
          VERIFY3U(vp->v_count, >=, vp->v_phantom_count);
          vp->v_phantom_count--;
          DTRACE_PROBE1(vn__phantom_rele, vnode_t *, vp);
          if (vp->v_count == 1) {
                  ASSERT0(vp->v_phantom_count);
                  mutex_exit(&vp->v_lock);
                  VOP_INACTIVE(vp, CRED(), NULL);
                  return;
+         } else {
+                 VERIFY(vp->v_count > 0);
          }
          VN_RELE_LOCKED(vp);
          mutex_exit(&vp->v_lock);
  }
  
*** 891,902 ****
   * only by the DNLC.
   */
  void
  vn_rele_dnlc(vnode_t *vp)
  {
-         VERIFY((vp->v_count > 0) && (vp->v_count_dnlc > 0));
          mutex_enter(&vp->v_lock);
          if (--vp->v_count_dnlc == 0) {
                  if (vp->v_count == 1) {
                          mutex_exit(&vp->v_lock);
                          VOP_INACTIVE(vp, CRED(), NULL);
                          return;
--- 893,904 ----
   * only by the DNLC.
   */
  void
  vn_rele_dnlc(vnode_t *vp)
  {
          mutex_enter(&vp->v_lock);
+         VERIFY((vp->v_count > 0) && (vp->v_count_dnlc > 0));
          if (--vp->v_count_dnlc == 0) {
                  if (vp->v_count == 1) {
                          mutex_exit(&vp->v_lock);
                          VOP_INACTIVE(vp, CRED(), NULL);
                          return;
*** 914,930 ****
   * path from accessing a stream head that is going away.
   */
  void
  vn_rele_stream(vnode_t *vp)
  {
-         VERIFY(vp->v_count > 0);
          mutex_enter(&vp->v_lock);
          vp->v_stream = NULL;
          if (vp->v_count == 1) {
                  mutex_exit(&vp->v_lock);
                  VOP_INACTIVE(vp, CRED(), NULL);
                  return;
          }
          VN_RELE_LOCKED(vp);
          mutex_exit(&vp->v_lock);
  }
  
--- 916,933 ----
   * path from accessing a stream head that is going away.
   */
  void
  vn_rele_stream(vnode_t *vp)
  {
          mutex_enter(&vp->v_lock);
          vp->v_stream = NULL;
          if (vp->v_count == 1) {
                  mutex_exit(&vp->v_lock);
                  VOP_INACTIVE(vp, CRED(), NULL);
                  return;
+         } else {
+                 VERIFY(vp->v_count > 0);
          }
          VN_RELE_LOCKED(vp);
          mutex_exit(&vp->v_lock);
  }
  
*** 945,961 ****
   * This is because taskqs throttle back allocation if too many are created.
   */
  void
  vn_rele_async(vnode_t *vp, taskq_t *taskq)
  {
-         VERIFY(vp->v_count > 0);
          mutex_enter(&vp->v_lock);
          if (vp->v_count == 1) {
                  mutex_exit(&vp->v_lock);
                  VERIFY(taskq_dispatch(taskq, (task_func_t *)vn_rele_inactive,
                      vp, TQ_SLEEP) != TASKQID_INVALID);
                  return;
          }
          VN_RELE_LOCKED(vp);
          mutex_exit(&vp->v_lock);
  }
  
--- 948,965 ----
   * This is because taskqs throttle back allocation if too many are created.
   */
  void
  vn_rele_async(vnode_t *vp, taskq_t *taskq)
  {
          mutex_enter(&vp->v_lock);
          if (vp->v_count == 1) {
                  mutex_exit(&vp->v_lock);
                  VERIFY(taskq_dispatch(taskq, (task_func_t *)vn_rele_inactive,
                      vp, TQ_SLEEP) != TASKQID_INVALID);
                  return;
+         } else {
+                 VERIFY(vp->v_count > 0);
          }
          VN_RELE_LOCKED(vp);
          mutex_exit(&vp->v_lock);
  }