5269 zfs: zpool import slow
PORTING: this code relies on the property of taskq_wait to wait
until no more tasks are queued and no more tasks are active. As
we always queue new tasks from within other tasks, task_wait
reliably waits for the full recursion to finish, even though we
enqueue new tasks after taskq_wait has been called.
On platforms other than illumos, taskq_wait may not have this
property.
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Reviewed by: George Wilson <george.wilson@delphix.com>

*** 756,766 ****
  {
          ASSERT(dmu_tx_is_syncing(tx));
          ASSERT(dp->dp_origin_snap != NULL);
  
          VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj, upgrade_clones_cb,
!             tx, DS_FIND_CHILDREN));
  }
  
  /* ARGSUSED */
  static int
  upgrade_dir_clones_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
--- 756,766 ----
  {
          ASSERT(dmu_tx_is_syncing(tx));
          ASSERT(dp->dp_origin_snap != NULL);
  
          VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj, upgrade_clones_cb,
!             tx, DS_FIND_CHILDREN | DS_FIND_SERIALIZE));
  }
  
  /* ARGSUSED */
  static int
  upgrade_dir_clones_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
*** 810,820 ****
          VERIFY0(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
              DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx));
          VERIFY0(bpobj_open(&dp->dp_free_bpobj, dp->dp_meta_objset, obj));
  
          VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
!             upgrade_dir_clones_cb, tx, DS_FIND_CHILDREN));
  }
  
  void
  dsl_pool_create_origin(dsl_pool_t *dp, dmu_tx_t *tx)
  {
--- 810,820 ----
          VERIFY0(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
              DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx));
          VERIFY0(bpobj_open(&dp->dp_free_bpobj, dp->dp_meta_objset, obj));
  
          VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
!             upgrade_dir_clones_cb, tx, DS_FIND_CHILDREN | DS_FIND_SERIALIZE));
  }
  
  void
  dsl_pool_create_origin(dsl_pool_t *dp, dmu_tx_t *tx)
  {
*** 1054,1058 ****
--- 1054,1064 ----
  boolean_t
  dsl_pool_config_held(dsl_pool_t *dp)
  {
          return (RRW_LOCK_HELD(&dp->dp_config_rwlock));
  }
+ 
+ boolean_t
+ dsl_pool_config_held_writer(dsl_pool_t *dp)
+ {
+         return (RRW_WRITE_HELD(&dp->dp_config_rwlock));
+ }