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[Chris J Arges <1524069@xxxxxxxxxxxxxxxxxx>]

Ok I attempted to reproduce without success. What I tried:
- Xenial on Xenial on machine/guest with avx2
- Trusty 3.13.0-{68,71} on Xenial on machine/guest with avx2

In both of these instances I modprobed raid6_pq, in the trusty instance
I triggered an upgrade from 68 to 71 and neither of these caused a
segfault.

The following information would be useful in debugging this:

1) The differences between the guests /proc/cpuinfo with it reproducing and not-reproducing. This can verify the avx2 bit is to blame.
2) Can you simply 'sudo modprobe -r raid6_pq && sudo modprobe raid6_pq' to trigger this issue?
3) Can you test with a xenial guest and a similar configuration to see if this still triggers the issue?
4) If you have the ability testing with different versions of hypervisor (trusty vs xenial) might also be useful.

Thanks,
--chris j arges

** Changed in: linux (Ubuntu)
     Assignee: (unassigned) => Chris J Arges (arges)

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https://bugs.launchpad.net/bugs/1524069

Title:
  [Xenial] KVM trusty guest 3.13.0-68 raid6-pq panic in
  raid6_avx21_gen_syndrome() while probing grub devices [was: Xenial
  KVM: updating Trusty guest from 3.13.0-68 to 3.13.0-71 causes kernel
  exception]

Status in kvm package in Ubuntu:
  New
Status in linux package in Ubuntu:
  Confirmed

Bug description:
  The symptom I saw was this (note the segfault, and apt-get upgrade
  hangs after this):

  Setting up linux-image-3.13.0-71-generic (3.13.0-71.114) ...
  Running depmod.
  update-initramfs: deferring update (hook will be called later)
  Examining /etc/kernel/postinst.d.
  run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 3.13.0-71-generic /boot/vmlinuz-3.13.0-71-generic
  run-parts: executing /etc/kernel/postinst.d/initramfs-tools 3.13.0-71-generic /boot/vmlinuz-3.13.0-71-generic
  update-initramfs: Generating /boot/initrd.img-3.13.0-71-generic
  run-parts: executing /etc/kernel/postinst.d/pm-utils 3.13.0-71-generic /boot/vmlinuz-3.13.0-71-generic
  run-parts: executing /etc/kernel/postinst.d/zz-update-grub 3.13.0-71-generic /boot/vmlinuz-3.13.0-71-generic
  Generating grub configuration file ...
  Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.
  Found linux image: /boot/vmlinuz-3.13.0-71-generic
  Found initrd image: /boot/initrd.img-3.13.0-71-generic
  Found linux image: /boot/vmlinuz-3.13.0-68-generic
  Found initrd image: /boot/initrd.img-3.13.0-68-generic
  Segmentation fault
  done
  Setting up linux-firmware (1.127.19) ...
  Setting up linux-image-extra-3.13.0-71-generic (3.13.0-71.114) ...
  run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 3.13.0-71-generic /boot/vmlinuz-3.13.0-71-generic
  run-parts: executing /etc/kernel/postinst.d/initramfs-tools 3.13.0-71-generic /boot/vmlinuz-3.13.0-71-generic
  update-initramfs: Generating /boot/initrd.img-3.13.0-71-generic
  run-parts: executing /etc/kernel/postinst.d/pm-utils 3.13.0-71-generic /boot/vmlinuz-3.13.0-71-generic
  run-parts: executing /etc/kernel/postinst.d/zz-update-grub 3.13.0-71-generic /boot/vmlinuz-3.13.0-71-generic
  Generating grub configuration file ...
  Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.
  Found linux image: /boot/vmlinuz-3.13.0-71-generic
  Found initrd image: /boot/initrd.img-3.13.0-71-generic
  Found linux image: /boot/vmlinuz-3.13.0-68-generic
  Found initrd image: /boot/initrd.img-3.13.0-68-generic

  In dmesg, I saw a corresponding kernel stack trace:

  [  522.649091] SGI XFS with ACLs, security attributes, realtime, large block/inode numbers, no debug enabled
  [  522.654031] JFS: nTxBlock = 8192, nTxLock = 65536
  [  522.660515] NTFS driver 2.1.30 [Flags: R/O MODULE].
  [  522.672519] QNX4 filesystem 0.2.3 registered.
  [  522.677257] xor: measuring software checksum speed
  [  522.715613]    prefetch64-sse: 17306.000 MB/sec
  [  522.755589]    generic_sse: 16039.000 MB/sec
  [  522.755590] xor: using function: prefetch64-sse (17306.000 MB/sec)
  [  522.823619] raid6: sse2x1   10481 MB/s
  [  522.891614] raid6: sse2x2   13303 MB/s
  [  522.959616] raid6: sse2x4   15209 MB/s
  [  522.963634] invalid opcode: 0000 [#1] SMP 
  [  522.963645] Modules linked in: raid6_pq(+) xor ufs qnx4 hfsplus hfs minix ntfs msdos jfs xfs libcrc32c ipt_MASQUERADE iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT xt_CHECKSUM iptable_mangle xt_tcpudp bridge stp llc ip6table_filter ip6_tables iptable_filter ip_tables ebtable_nat ebtables x_tables snd_hda_intel snd_hda_codec snd_hwdep qxl snd_pcm kvm_intel ttm snd_page_alloc kvm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel drm_kms_helper snd_timer aesni_intel snd aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd drm soundcore lp parport serio_raw i2c_piix4 mac_hid pata_acpi floppy psmouse
  [  522.963746] CPU: 2 PID: 11288 Comm: modprobe Not tainted 3.13.0-68-generic #111-Ubuntu
  [  522.963751] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
  [  522.963755] task: ffff880059363000 ti: ffff88005dec6000 task.ti: ffff88005dec6000
  [  522.963759] RIP: 0010:[<ffffffffa049dd0a>]  [<ffffffffa049dd0a>] raid6_avx21_gen_syndrome+0x4a/0x160 [raid6_pq]
  [  522.963767] RSP: 0018:ffff88005dec7c40  EFLAGS: 00010246
  [  522.963771] RAX: 0000000000000000 RBX: ffff88005dec7c88 RCX: ffff880059363000
  [  522.963774] RDX: 0000000000000000 RSI: 0000000000000080 RDI: 0000000000000012
  [  522.963778] RBP: ffff88005dec7c70 R08: 0000000000000086 R09: 000000000000025f
  [  522.963781] R10: 0000000000000000 R11: ffff88005dec79ae R12: 0000000000001000
  [  522.963785] R13: ffff880043a42000 R14: ffff880043a43000 R15: 0000000000000012
  [  522.963789] FS:  00007fa330823740(0000) GS:ffff88007fd00000(0000) knlGS:0000000000000000
  [  522.963793] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  [  522.963796] CR2: 00007fa330623000 CR3: 0000000036acf000 CR4: 00000000001006e0
  [  522.963801] Stack:
  [  522.963803]  0000000000000080 ffffffffa049e238 ffffffffa04b0720 ffff880043a42000
  [  522.963810]  0000000000003cd7 000000010000d992 ffff88005dec7d40 ffffffffa00d20fb
  [  522.963817]  0000000000000000 ffffffffa04a0600 ffffffffa04a1600 ffffffffa04a2600
  [  522.963824] Call Trace:
  [  522.963838]  [<ffffffffa00d20fb>] init_module+0xfb/0x1000 [raid6_pq]
  [  522.963843]  [<ffffffffa00d2000>] ? 0xffffffffa00d1fff
  [  522.963849]  [<ffffffff8100214a>] do_one_initcall+0xfa/0x1b0
  [  522.963854]  [<ffffffff81059903>] ? set_memory_nx+0x43/0x50
  [  522.963859]  [<ffffffff810e29bd>] load_module+0x12dd/0x1b40
  [  522.963863]  [<ffffffff810de440>] ? store_uevent+0x40/0x40
  [  522.963868]  [<ffffffff810e3396>] SyS_finit_module+0x86/0xb0
  [  522.963873]  [<ffffffff81734cdd>] system_call_fastpath+0x1a/0x1f
  [  522.963876] Code: 00 00 00 00 53 48 89 d3 48 83 ec 08 48 89 75 d0 4c 8b 2c c2 4c 8b 74 32 08 e8 13 f9 b7 e0 84 c0 0f 84 f1 00 00 00 e8 c6 f9 b7 e0 <c5> fd 6f 05 ee 2a 01 00 c5 e5 ef db 4d 85 e4 0f 84 c0 00 00 00 
  [  522.963940] RIP  [<ffffffffa049dd0a>] raid6_avx21_gen_syndrome+0x4a/0x160 [raid6_pq]
  [  522.963946]  RSP <ffff88005dec7c40>
  [  522.963949] ---[ end trace 7324d498bc862f81 ]---

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: linux-image-3.13.0-68-generic 3.13.0-68.111
  ProcVersionSignature: Ubuntu 3.13.0-68.111-generic 3.13.11-ckt27
  Uname: Linux 3.13.0-68-generic x86_64
  AlsaVersion: Advanced Linux Sound Architecture Driver Version k3.13.0-68-generic.
  AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
  ApportVersion: 2.14.1-0ubuntu3.19
  Architecture: amd64
  ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/by-path', '/dev/snd/controlC0', '/dev/snd/hwC0D0', '/dev/snd/pcmC0D0c', '/dev/snd/pcmC0D0p', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
  CRDA: Error: [Errno 2] No such file or directory: 'iw'
  Card0.Amixer.info: Error: [Errno 2] No such file or directory: 'amixer'
  Card0.Amixer.values: Error: [Errno 2] No such file or directory: 'amixer'
  Date: Tue Dec  8 13:08:13 2015
  HibernationDevice: RESUME=UUID=69fc2e53-278d-40ca-8109-64f826a073e7
  IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
  Lsusb:
   Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
   Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
   Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
   Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
  MachineType: QEMU Standard PC (i440FX + PIIX, 1996)
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcFB: 0 qxldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-68-generic root=UUID=897d5dd8-599e-42f9-a081-96f73cef59d9 ro splash quiet vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-3.13.0-68-generic N/A
   linux-backports-modules-3.13.0-68-generic  N/A
   linux-firmware                             1.127.19
  RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 04/01/2014
  dmi.bios.vendor: SeaBIOS
  dmi.bios.version: Ubuntu-1.8.2-1ubuntu1
  dmi.chassis.type: 1
  dmi.chassis.vendor: QEMU
  dmi.chassis.version: pc-i440fx-wily
  dmi.modalias: dmi:bvnSeaBIOS:bvrUbuntu-1.8.2-1ubuntu1:bd04/01/2014:svnQEMU:pnStandardPC(i440FX+PIIX,1996):pvrpc-i440fx-wily:cvnQEMU:ct1:cvrpc-i440fx-wily:
  dmi.product.name: Standard PC (i440FX + PIIX, 1996)
  dmi.product.version: pc-i440fx-wily
  dmi.sys.vendor: QEMU

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