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[Jürg Häfliger <1826385@xxxxxxxxxxxxxxxxxx>]

** Tags added: kernel-daily-bug

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https://bugs.launchpad.net/bugs/1826385

Title:
  ftrace in ubuntu_kernel_selftests hang with Cosmic kernel

Status in ubuntu-kernel-tests:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Bionic:
  Fix Released
Status in linux source package in Cosmic:
  Fix Released

Bug description:
  == Justification ==
  Running the ftrace in ubuntu_kernel_selftests repetitively against x86 Cosmic kernel will cause system hang.

  When this happens, you won't be able to ssh into this system, and no
  log can be found in syslog.

  This hang is caused by one of the sub-test: kprobe/multiple_kprobes

  Masami's comment from upstream discussion (https://lkml.org/lkml/2018/12/3/1219):
  In arch/x86/kernel/kprobes/opt.c, copy_optimized_instructions() does a copy loop, but only update src and dest cursors, but not update real address which is used for adjusting RIP relative instruction.

  == Fix ==
  43a1b0cb4 (kprobes/x86: Fix instruction patching corruption when copying more than one RIP-relative instruction)

  This patch is already in D.
  For B/C, they all have this ill-commit 63fef14 and this patch can be cherry-picked. Note that for Bionic kernel it can only be triggered in this way with a kernel built with GCC-8.

  Although it's a bit difficult to trigger this on Bionic, I think it
  worth this fix as it's quite straightforward.

  For X, the ill-commit 63fef14 does not exist.

  == Test ==
  Test kernel for Cosmic and Bionic built with GCC-8:
  http://people.canonical.com/~phlin/kernel/lp-1826385-ftrace-hang/

  (To verify this for the Bionic, you will need to build a kernel with
  GCC-8.)

  Patch tested with a bare-metal and a KVM node, both of them can pass
  the beating repetitively.

  == Regression Potential ==
  Low, upstream fix specific for kprobe and limited to x86 architecture.


  == Original Bug Report ==
  This issue is a bit strange.

  The test has passed with Cosmic 4.18.0-18.19 generic kernel on AMD64
  node during our SRU testing process.

  https://pastebin.ubuntu.com/p/HN2vN6fCXn/

  However, Tyler found that this test will hang after:
  [30] Kretprobe dynamic event with maxactive	[PASS]
  [31] Register/unregister many kprobe events	[PASS]

  And this is 100% reproducible.

  No relevant output in syslog.

  This will need further investigation.

  ProblemType: Bug
  DistroRelease: Ubuntu 18.10
  Package: linux-image-4.18.0-18-generic 4.18.0-18.19
  ProcVersionSignature: User Name 4.18.0-18.19-generic 4.18.20
  Uname: Linux 4.18.0-18-generic x86_64
  AlsaDevices:
   total 0
   crw-rw---- 1 root audio 116,  1 Apr 25 07:16 seq
   crw-rw---- 1 root audio 116, 33 Apr 25 07:16 timer
  AplayDevices: Error: [Errno 2] No such file or directory: 'aplay': 'aplay'
  ApportVersion: 2.20.10-0ubuntu13.2
  Architecture: amd64
  ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord': 'arecord'
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
  Date: Thu Apr 25 07:18:51 2019
  IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig': 'iwconfig'
  Lsusb: Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
  MachineType: QEMU Standard PC (i440FX + PIIX, 1996)
  PciMultimedia:

  ProcFB: 0 cirrusdrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.18.0-18-generic root=UUID=2f68c627-8ab4-40d5-8c06-6563436d0f96 ro
  RelatedPackageVersions:
   linux-restricted-modules-4.18.0-18-generic N/A
   linux-backports-modules-4.18.0-18-generic  N/A
   linux-firmware                             1.175.3
  RfKill: Error: [Errno 2] No such file or directory: 'rfkill': '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-xenial
  dmi.modalias: dmi:bvnSeaBIOS:bvrUbuntu-1.8.2-1ubuntu1:bd04/01/2014:svnQEMU:pnStandardPC(i440FX+PIIX,1996):pvrpc-i440fx-xenial:cvnQEMU:ct1:cvrpc-i440fx-xenial:
  dmi.product.name: Standard PC (i440FX + PIIX, 1996)
  dmi.product.version: pc-i440fx-xenial
  dmi.sys.vendor: QEMU

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