This issue has been reported by Alan Somers as
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225877

dmu_objset_refresh_ownership() first disowns a dataset (and releases
it) and then owns it again. There is an assert that the new dataset
object is the same as the old dataset object.  When running ZFS Test
Suite on FreeBSD we see this panic from zpool_upgrade_007_pos test:

panic: solaris assert: newds == os->os_dsl_dataset (0xfffff80045f4c000
== 0xfffff80021ab4800)

I see that the old dataset has dsl_dataset_evict_async() pending in
ds_dbu.dbu_tqent and its ds_dbuf is NULL.