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[Colin Ian King <1531768@xxxxxxxxxxxxxxxxxx>]

Finally able to trip a rcu timeout.  3.19.0-61-generic kernel on host,
xenial on server, host busy on async i/o requests (via stress-ng):

[  825.195520] systemd[1]: Started Journal Service.
[  900.108730] INFO: rcu_sched detected stalls on CPUs/tasks:
[  900.110254] 	0-...: (4 GPs behind) idle=750/0/0 softirq=4668/4668 fqs=1 
[  900.111742] 	(detected by 2, t=15002 jiffies, g=1980, c=1979, q=90)
[  900.113384] Call trace:
[  900.114035] rcu_sched kthread starved for 15001 jiffies! g1980 c1979 f0x0 s3 ->state=0x1
[  900.108730] INFO: rcu_sched detected stalls on CPUs/tasks:
[  900.110254] 	0-...: (4 GPs behind) idle=750/0/0 softirq=4668/4668 fqs=1 
[  900.111742] 	(detected by 2, t=15002 jiffies, g=1980, c=1979, q=90)
[  900.113366] Task dump for CPU 0:
[  900.113375] swapper/0       R  running task        0     0      0 0x00000000
[  900.113384] Call trace:
[  900.113987] [<ffff800000086ad0>] __switch_to+0x90/0xa8
[  900.113999] [<ffff800000143c40>] __tick_nohz_idle_enter+0x50/0x3f0
[  900.114003] [<ffff800000144238>] tick_nohz_idle_enter+0x40/0x70
[  900.114010] [<ffff80000010b8b0>] cpu_startup_entry+0x288/0x2d8
[  900.114018] [<ffff8000008f18f0>] rest_init+0x80/0x88
[  900.114025] [<ffff800000cb59f8>] start_kernel+0x3e8/0x414
[  900.114029] [<00000000408fb000>] 0x408fb000
[  900.114035] rcu_sched kthread starved for 15001 jiffies! g1980 c1979 f0x0 s3 ->state=0x1

Let me see if I can repro this on other kernels now

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https://bugs.launchpad.net/bugs/1531768

Title:
  [arm64] lockups some time after booting

Status in Auto Package Testing:
  Triaged
Status in linux package in Ubuntu:
  Confirmed

Bug description:
  I created an 8 CPU arm64 instance on Canonical's Scalingstack (which I
  want to use for armhf autopkgtesting in LXD). I started with wily as
  that has lxd available (it's not yet available in trusty nor the PPA
  for arm64).

  However, pretty much any LXD task that I do (I haven't tried much
  else) on this machine takes unbearably long. A simple "lxc profile set
  default raw.lxc lxc.seccomp=" or "lxc list" takes several minutes.

  I see tons of

  [ 1020.971955] rcu_sched kthread starved for 6000 jiffies! g1095 c1094 f0x0
  [ 1121.166926] INFO: task fsnotify_mark:69 blocked for more than 120 seconds.

  in dmesg (the attached apport info has the complete dmesg).

  ProblemType: Bug
  DistroRelease: Ubuntu 15.10
  Package: linux-image-4.2.0-22-generic 4.2.0-22.27
  ProcVersionSignature: User Name 4.2.0-22.27-generic 4.2.6
  Uname: Linux 4.2.0-22-generic aarch64
  AlsaDevices:
   total 0
   crw-rw---- 1 root audio 116,  1 Jan  7 09:18 seq
   crw-rw---- 1 root audio 116, 33 Jan  7 09:18 timer
  AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
  ApportVersion: 2.19.1-0ubuntu5
  Architecture: arm64
  ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
  CRDA: N/A
  Date: Thu Jan  7 09:24:01 2016
  IwConfig:
   eth0      no wireless extensions.

   lo        no wireless extensions.

   lxcbr0    no wireless extensions.
  Lspci:
   00:00.0 Host bridge [0600]: Red Hat, Inc. Device [1b36:0008]
    Subsystem: Red Hat, Inc Device [1af4:1100]
    Control: I/O- Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
    Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
  Lsusb: Error: command ['lsusb'] failed with exit code 1: unable to initialize libusb: -99
  PciMultimedia:

  ProcEnviron:
   TERM=screen
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcFB:

  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.2.0-22-generic root=LABEL=cloudimg-rootfs earlyprintk
  RelatedPackageVersions:
   linux-restricted-modules-4.2.0-22-generic N/A
   linux-backports-modules-4.2.0-22-generic  N/A
   linux-firmware                            1.149.3
  RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
  SourcePackage: linux
  UdevLog: Error: [Errno 2] No such file or directory: '/var/log/udev'
  UpgradeStatus: No upgrade log present (probably fresh install)

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