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, 3 insertions, 0 deletions

diff --git a/cddl/contrib/opensolaris/cmd/ztest/ztest.c b/cddl/contrib/opensolaris/cmd/ztest/ztest.c
index 1458dbc..74e63aa 100644
--- a/cddl/contrib/opensolaris/cmd/ztest/ztest.c
+++ b/cddl/contrib/opensolaris/cmd/ztest/ztest.c
@@ -3607,6 +3607,9 @@ ztest_dmu_read_write(ztest_ds_t *zd, uint64_t id)
 	else
 		dmu_tx_hold_write(tx, bigobj, bigoff, bigsize);
 
+	/* This accounts for setting the checksum/compression. */
+	dmu_tx_hold_bonus(tx, bigobj);
+
 	txg = ztest_tx_assign(tx, TXG_MIGHTWAIT, FTAG);
 	if (txg == 0) {
 		umem_free(packbuf, packsize);