6537 Panic on zpool scrub with DEBUG kernel

*** 19,28 ****
--- 19,29 ----
   * CDDL HEADER END
   */
  /*
   * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
+  * Copyright 2016 Gary Mills
   */
  
  #include <sys/dsl_scan.h>
  #include <sys/dsl_pool.h>
  #include <sys/dsl_dataset.h>
*** 1502,1512 ****
                   */
                  ddt_sync(spa, tx->tx_txg);
          }
          if (err != 0)
                  return;
!         if (!scn->scn_async_destroying && zfs_free_leak_on_eio &&
              (dsl_dir_phys(dp->dp_free_dir)->dd_used_bytes != 0 ||
              dsl_dir_phys(dp->dp_free_dir)->dd_compressed_bytes != 0 ||
              dsl_dir_phys(dp->dp_free_dir)->dd_uncompressed_bytes != 0)) {
                  /*
                   * We have finished background destroying, but there is still
--- 1503,1514 ----
                   */
                  ddt_sync(spa, tx->tx_txg);
          }
          if (err != 0)
                  return;
!         if (dp->dp_free_dir != NULL && !scn->scn_async_destroying &&
!             zfs_free_leak_on_eio && 
              (dsl_dir_phys(dp->dp_free_dir)->dd_used_bytes != 0 ||
              dsl_dir_phys(dp->dp_free_dir)->dd_compressed_bytes != 0 ||
              dsl_dir_phys(dp->dp_free_dir)->dd_uncompressed_bytes != 0)) {
                  /*
                   * We have finished background destroying, but there is still
*** 1528,1538 ****
                  dsl_dir_diduse_space(dp->dp_free_dir, DD_USED_HEAD,
                      -dsl_dir_phys(dp->dp_free_dir)->dd_used_bytes,
                      -dsl_dir_phys(dp->dp_free_dir)->dd_compressed_bytes,
                      -dsl_dir_phys(dp->dp_free_dir)->dd_uncompressed_bytes, tx);
          }
!         if (!scn->scn_async_destroying) {
                  /* finished; verify that space accounting went to zero */
                  ASSERT0(dsl_dir_phys(dp->dp_free_dir)->dd_used_bytes);
                  ASSERT0(dsl_dir_phys(dp->dp_free_dir)->dd_compressed_bytes);
                  ASSERT0(dsl_dir_phys(dp->dp_free_dir)->dd_uncompressed_bytes);
          }
--- 1530,1540 ----
                  dsl_dir_diduse_space(dp->dp_free_dir, DD_USED_HEAD,
                      -dsl_dir_phys(dp->dp_free_dir)->dd_used_bytes,
                      -dsl_dir_phys(dp->dp_free_dir)->dd_compressed_bytes,
                      -dsl_dir_phys(dp->dp_free_dir)->dd_uncompressed_bytes, tx);
          }
!         if (dp->dp_free_dir != NULL && !scn->scn_async_destroying) {
                  /* finished; verify that space accounting went to zero */
                  ASSERT0(dsl_dir_phys(dp->dp_free_dir)->dd_used_bytes);
                  ASSERT0(dsl_dir_phys(dp->dp_free_dir)->dd_compressed_bytes);
                  ASSERT0(dsl_dir_phys(dp->dp_free_dir)->dd_uncompressed_bytes);
          }