'zfs recv' hangs when receiving from a FreeBSD zfs

[Patrick Meyer]

When creating a pool snapshot on a freenas/freebsd like this:

```
root@freenas:~ # uname -a
FreeBSD freenas.local 11.0-STABLE FreeBSD 11.0-STABLE #0 r321665+25fe8ba8d06(freenas/11.0-stable): Mon Sep 25 06:24:11 UTC 2017 root@gauntlet:/freenas-11-releng/freenas/_BE/objs/freenas-11-releng/freenas/_BE/os/sys/FreeNAS.amd64 amd64
freenas# zpool create tank gptid/62a26be7-cd4a-11e7-927b-0800278dcda9
freenas# dd if=/dev/zero of=/tank/ur.bin bs=64K count=1
freenas# zfs snap tank@example
```

And trying to `zfs send | zfs recv` it to an ubuntu zfs like this:
```
space@ubuntu:~$ apt-cache policy zfsutils-linux
zfsutils-linux:
  Installed: 0.6.5.11-1ubuntu3
  Candidate: 0.6.5.11-1ubuntu3
  Version table:
 *** 0.6.5.11-1ubuntu3 500
        500 http://us.archive.ubuntu.com/ubuntu artful/main amd64 Packages
        100 /var/lib/dpkg/status
space@ubuntu:~$ lsb_release -rd
Description: Ubuntu 17.10
Release: 17.10

root@ubuntu:~$ ssh root@freenas zfs send tank@example > freenas11.zfssend
root@ubuntu:~# cat ./freenas11.zfssend | zfs recv tank/something
```

The `zfs recv` process burns 100% CPU and hangs forever. I have attached an example freenas11.zfssend file, though it's easily reproduced.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: zfsutils-linux 0.6.5.11-1ubuntu3
ProcVersionSignature: Ubuntu 4.13.0-16.19-generic 4.13.4
Uname: Linux 4.13.0-16-generic x86_64
NonfreeKernelModules: zfs zunicode zavl zcommon znvpair
ApportVersion: 2.20.7-0ubuntu3
Architecture: amd64
Date: Sun Nov 19 22:10:15 2017
ExecutablePath: /sbin/zfs
InstallationDate: Installed on 2017-11-17 (2 days ago)
InstallationMedia: Ubuntu-Server 17.10 "Artful Aardvark" - Release amd64 (20171017.1)
ProcEnviron:
 LANG=en_US.UTF-8
 SHELL=/bin/bash
 TERM=xterm-256color
 PATH=(custom, no user)
SourcePackage: zfs-linux
UpgradeStatus: No upgrade log present (probably fresh install)

[Fabian Grünbichler (f-gruenbichler)]

see https://github.com/zfsonlinux/zfs/pull/6616 for the fix in ZFS on Linux 0.7.3 (on the sender side). not yet backported to Open-ZFS, and thus not in FreeBSDs ZFS either.

this is not really a bug in ZFS on the receiver side, it was an accidental break of backwards compatibility.

[Fabian Grünbichler (f-gruenbichler)]

but, upgrading ZFS to 0.7.x would fix it on the receiving side, so that might be an option for you ;)

[Patrick Meyer (herrspace)]

Hmm, using an untested Ubuntu ZOL or even building my own ZOL is not really why I want to use Ubuntu ;) I understand that this is a Problem caused by Open-ZFS, you should consider backporting that ZOL patch to make migration to Ubuntu easier though.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Colin Ian King (colin-king)]

@Fabian, do you have any references to the fix than can backported to pre-0.7.5 (pre-Ubuntu Bionic) releases ZFS so I can easily apply/backport these. I'm a little confused of which exact patch(es) are required.

Thanks. Colin.

[Colin Ian King (colin-king)]

Ubuntu 17.10 is now end-of-life. However, this is fixed in Ubuntu 18.04 with ZFS 0.7.5, so please consider using this now.