MFV r254071:

Fix a regression introduced by fix for Illumos bug #3834.  Quote from
Matthew Ahrens on the Illumos issue:

ztest fails this assertion because ztest_dmu_read_write() does
        dmu_tx_hold_free(tx, bigobj, bigoff, bigsize);
and then
    dmu_object_set_checksum(os, bigobj,
        (enum zio_checksum)ztest_random_dsl_prop(ZFS_PROP_CHECKSUM), tx);

If the region to free is past the end of the file, the DMU assumes that there
will be nothing to do for this object.  However, ztest does set_checksum(),
which must modify the dnode.  The fix is for ztest to also call

    dmu_tx_hold_bonus(tx, bigobj);

so we can account for the dirty data associated with setting the checksum

Illumos ZFS issues:
  3955 ztest failure: assertion refcount_count(&tx->tx_space_written)
         + delta <= tx->tx_space_towrite

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c
index 929b0c4..8d23aa3 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c
@@ -448,12 +448,12 @@ dmu_tx_count_free(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
 		blkid = off >> dn->dn_datablkshift;
 		nblks = (len + dn->dn_datablksz - 1) >> dn->dn_datablkshift;
 
-		if (blkid >= dn->dn_maxblkid) {
+		if (blkid > dn->dn_maxblkid) {
 			rw_exit(&dn->dn_struct_rwlock);
 			return;
 		}
 		if (blkid + nblks > dn->dn_maxblkid)
-			nblks = dn->dn_maxblkid - blkid;
+			nblks = dn->dn_maxblkid - blkid + 1;
 
 	}
 	l0span = nblks;    /* save for later use to calc level > 1 overhead */