[Pkg-zfsonlinux-devel] Bug#1009242: zfs-dkms: PPC get_user workaround breaks boot on ZFS root

[Nathaniel Wesley Filardo]

Package: zfs-dkms
Version: 2.1.2-1~bpo11+1
Severity: critical
Tags: patch
Justification: breaks the whole system
X-Debbugs-Cc: nwfilardo at gmail.com

Dear Maintainer,

Presently (and since 16 Nov 2021), the Debian ZFS repo has been carrying Colin
Ian King's
https://salsa.debian.org/zfsonlinux-team/zfs/-/blob/master/debian/patches/4900-ppc-get-user-workaround.patch
to work around a build failure on PPC machines whose kernels post-date
7613f5a66becfd0e43a0f34de8518695888f5458 ("powerpc/64s/kuap: Use
mmu_has_feature()").  5.13 is the first release to contain that patch
(amusingly, someone noticed pretty quickly: https://lwn.net/Articles/856312/).

Unfortunately, while this does fix the compilation error, in a rather
heavy-handed way, it results in the system hanging at boot, well before reaching
the multi-user target.  The EFAULT returned to userspace simply triggers a
retry, and so we spin.  As I am on a Debian kernel after 5.13, I am unable to
upgrade my ZFS pacakges and keep a working system without rolling back to an
older kernel, which I cannot readily do, due to another bug in pre-5.15 PPC
kernel packages: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=990279 .

I reached out to the original author of mmu_feature_keys, and he has agreed to
change the EXPORT_SYMBOL status of this symbol.  His one-line patch to do so,
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20220329085709.4132729-1-haokexin@gmail.com/
has yet to be picked up by
https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/ , but, I
think, could be safely included in Debian's kernel patch set until it does.

Can I ask that the ZFS and linux package maintainers coordinate picking up Kevin
Hao's patch into the kernel package and dropping Colin Ian King's workaround
from the ZFS package?

I do not know if I should also raise a bug against the linux package; please
advise.

-- System Information:
Debian Release: 11.3
  APT prefers stable-updates
  APT policy: (991, 'stable-updates'), (990, 'stable'), (500, 'unstable-debug'), (500, 'stable-security'), (500, 'stable-debug'), (500, 'proposed-updates-debug'), (300, 'unstable')
Architecture: ppc64el (ppc64le)

Kernel: Linux 5.15.0-0.bpo.2-powerpc64le (SMP w/176 CPU threads)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages zfs-dkms depends on:
ii  debconf [debconf-2.0]  1.5.77
ii  dkms                   2.8.4-3
ii  file                   1:5.39-3
ii  libc6-dev [libc-dev]   2.31-13+deb11u3
ii  libpython3-stdlib      3.9.2-3
ii  lsb-release            11.1.0
ii  perl                   5.32.1-4+deb11u2
ii  python3-distutils      3.9.2-1

Versions of packages zfs-dkms recommends:
ii  linux-libc-dev  5.16.12-1~bpo11+1
ii  zfs-zed         2.1.2-1~bpo11+1
ii  zfsutils-linux  2.1.2-1~bpo11+1

Versions of packages zfs-dkms suggests:
ii  debhelper  13.3.4

-- debconf information:
  zfs-dkms/stop-build-for-unknown-kernel: true
* zfs-dkms/note-incompatible-licenses:
  zfs-dkms/stop-build-for-32bit-kernel: true