[Pkg-zfsonlinux-devel] Bug#940932: zfs-dkms: Reads from ZFS volumes cause system instability when SIMD acceleration is enabled.

[Alexander]

Package: zfs-dkms
Version: 0.8.1-4~bpo10+1
Severity: critical
Tags: upstream
Justification: causes serious data loss

Dear Maintainer,

recently I have noticed some instability on one of my machines.
The mprime (https://www.mersenne.org/download/) Torture Tests would occasionaly show errors like 

"FATAL ERROR: Rounding was 0.5, expected less than 0.4
Hardware failure detected, consult stress.txt file."

random commands would occasionaly segfault.

While trying to narrow down the problem I have replaced the PSU, RAM and the CPU. Multiple hour long runs of memtest86 did not show any problem.

Finally I was able to narrow down the reads from ZFS volumes as the trigger for the instability. 
Scrubbing the volume would cause mprime to error out especially quickly.

As a workaround I switched the SIMD acceleration off by piping "scalar" to 

/sys/module/zfs/parameters/zfs_vdev_raidz_impl and /sys/module/zcommon/parameters/zfs_fletcher_4_impl

and that made the system stable again.

Here are the details on the hardware I'm using:

Motherboard:	X470 GAMING PLUS (MS-7B79) 
		BIOS version: 7B79vAC
CPU:		Ryzen 5 2600 and Ryzen 5 2600X

Please let me know if I can provide any other useful information for this issue.

-- System Information:
Debian Release: 10.1
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.19.0-6-amd64 (SMP w/12 CPU cores)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8), LANGUAGE=de_DE.UTF-8 (charmap=UTF-8)
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]  1.5.71
ii  dkms                   2.6.1-4
ii  file                   1:5.35-4
ii  libc6-dev [libc-dev]   2.28-10
ii  libpython3-stdlib      3.7.3-1
ii  lsb-release            10.2019051400
ii  perl                   5.28.1-6
ii  python3-distutils      3.7.3-1

Versions of packages zfs-dkms recommends:
ii  linux-libc-dev  4.19.67-2
ii  zfs-zed         0.8.1-4~bpo10+1
ii  zfsutils-linux  0.8.1-4~bpo10+1

zfs-dkms suggests no packages.

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