This bug was fixed in the package zfs-linux - 0.6.5.6-0ubuntu29
--------------- zfs-linux (0.6.5.6-0ubuntu29) xenial; urgency=medium
* Fix race condition in zfs_iput_async (LP: #1916486) - Upstream ZFS fix 43eaef6de817 ("Fix zrele race in zrele_async that can cause hang")
-- Heitor Alves de Siqueira <email address hidden> Thu, 25 Feb 2021 18:21:48 +0000
This bug was fixed in the package zfs-linux - 0.6.5.6-0ubuntu29
---------------
zfs-linux (0.6.5.6-0ubuntu29) xenial; urgency=medium
* Fix race condition in zfs_iput_async (LP: #1916486)
- Upstream ZFS fix 43eaef6de817 ("Fix zrele race in zrele_async that can
cause hang")
-- Heitor Alves de Siqueira <email address hidden> Thu, 25 Feb 2021 18:21:48 +0000