3955 ztest failure: assertion refcount_count(&tx->tx_space_written) + delta <= tx->tx_space_towrite
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>

*** 446,461 ****
                  }
          } else {
                  blkid = off >> dn->dn_datablkshift;
                  nblks = (len + dn->dn_datablksz - 1) >> dn->dn_datablkshift;
  
!                 if (blkid >= dn->dn_maxblkid) {
                          rw_exit(&dn->dn_struct_rwlock);
                          return;
                  }
                  if (blkid + nblks > dn->dn_maxblkid)
!                         nblks = dn->dn_maxblkid - blkid;
  
          }
          l0span = nblks;    /* save for later use to calc level > 1 overhead */
          if (dn->dn_nlevels == 1) {
                  int i;
--- 446,461 ----
                  }
          } else {
                  blkid = off >> dn->dn_datablkshift;
                  nblks = (len + dn->dn_datablksz - 1) >> dn->dn_datablkshift;
  
!                 if (blkid > dn->dn_maxblkid) {
                          rw_exit(&dn->dn_struct_rwlock);
                          return;
                  }
                  if (blkid + nblks > dn->dn_maxblkid)
!                         nblks = dn->dn_maxblkid - blkid + 1;
  
          }
          l0span = nblks;    /* save for later use to calc level > 1 overhead */
          if (dn->dn_nlevels == 1) {
                  int i;