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[Bug 1349028] Re: getitimer returns it_value=0 erroneously


** Branch linked: lp:ubuntu/precise-proposed/linux-lts-trusty

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  getitimer returns it_value=0 erroneously

Status in “linux” package in Ubuntu:
  Fix Released
Status in “linux” source package in Trusty:
  Fix Committed
Status in “linux” source package in Utopic:
  Fix Released

Bug description:
  According to the 'getitimer()' man page: "The element it_value is set
  to the amount of time remaining on the timer, or zero if the  timer is
  disabled.  Similarly, it_interval is set to the reset value."

  As such the following Perl program should never exit:

      use Time::HiRes;
      $SIG{VTALRM} = sub { };
      Time::HiRes::setitimer(&Time::HiRes::ITIMER_VIRTUAL, 0.5, 0.4);
      while (1) {
          my @t = Time::HiRes::getitimer(&Time::HiRes::ITIMER_VIRTUAL);
          exit 0 if $t[0] == 0;

  and on linux-image 3.11.0-18-generic (and all other systems tested) it
  loops forever but 3.13.0-32-generic it exits.  Have not bisected
  between those kernels, nor am I likely to be able to do so soon.

  This Perl program shows the timer countdown:

  use Time::HiRes;
  my $r = [Time::HiRes::gettimeofday()];
  sub display {
      my ($desc) = @_;
      my @t = Time::HiRes::getitimer(&Time::HiRes::ITIMER_VIRTUAL);
      my $i = Time::HiRes::tv_interval($r);
      printf "%s: elasped=%.8f; time left=%.6f reset time=%.6f\n", $desc,
  $SIG{VTALRM} = sub {
  Time::HiRes::setitimer(&Time::HiRes::ITIMER_VIRTUAL, 0.5, 0.4);
  while (1) {

  on other (working) systems it gives:

  inloop: elasped=1.65178400; time left=0.001000 reset time=0.401000
  inloop: elasped=1.65184200; time left=0.001000 reset time=0.401000
  inloop: elasped=1.65186800; time left=0.001000 reset time=0.401000
  inloop: elasped=1.65192300; time left=0.001000 reset time=0.401000
  inloop: elasped=1.65198100; time left=0.001000 reset time=0.401000
  VTALRM: elasped=1.65209800; time left=0.400000 reset time=0.401000
  (end of file)

  but on the 3.13.0-32-generic or later kernel I get:

  inloop: elasped=0.54692100; time left=0.000033 reset time=0.400000
  inloop: elasped=0.54692800; time left=0.000026 reset time=0.400000
  inloop: elasped=0.54693500; time left=0.000020 reset time=0.400000
  inloop: elasped=0.54694100; time left=0.000013 reset time=0.400000
  inloop: elasped=0.54694800; time left=0.000007 reset time=0.400000
  inloop: elasped=0.54695500; time left=0.000000 reset time=0.400000
  inloop: elasped=0.54696200; time left=0.004000 reset time=0.400000
  VTALRM: elasped=0.55013600; time left=0.397062 reset time=0.400000
  (end of file)

  The reset time also looks dodgy.

  Hardware is an Intel Core i7-920 on Asus P6T Deluxe v2 (X58)
  motherboard and hasn't changed.

  Requested information:

  Ubuntu 3.13.0-32.57-generic

  Description:	Ubuntu 14.04.1 LTS
  Release:	14.04

  # apt-cache policy linux-image-generic
    Version table:
   *** 0
          500 http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
          500 http://us.archive.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages
          500 http://us.archive.ubuntu.com/ubuntu/ trusty-proposed/main amd64 Packages
          500 http://ppa.launchpad.net/canonical-kernel-team/ppa/ubuntu/ trusty/main amd64 Packages
          100 /var/lib/dpkg/status 0
          500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
  ApportVersion: 2.14.1-0ubuntu3.2
  Architecture: amd64
   /dev/snd/controlC1:  tivrusky   3009 F.... pulseaudio
   /dev/snd/controlC0:  tivrusky   3009 F.... pulseaudio
  DistroRelease: Ubuntu 14.04
  HibernationDevice: RESUME=UUID=c026abdc-9fee-425c-b5ae-020bf6ea2ad6
   eth0      no wireless extensions.
   eth1      no wireless extensions.
   lo        no wireless extensions.
  MachineType: System manufacturer System Product Name
  Package: linux (not installed)
  ProcFB: 0 radeondrmfb
  ProcKernelCmdLine: root=UUID=3ea7a4cb-eade-4906-b545-5133d8c14080 ro quiet splash
  ProcVersionSignature: Ubuntu 3.13.0-32.57-generic
   linux-restricted-modules-3.13.0-32-generic N/A
   linux-backports-modules-3.13.0-32-generic  N/A
   linux-firmware                             1.127.5
   0: hci0: Bluetooth
   	Soft blocked: no
   	Hard blocked: no
  Tags:  trusty
  Uname: Linux 3.13.0-32-generic x86_64
  UpgradeStatus: Upgraded to trusty on 2014-06-10 (46 days ago)
  UserGroups: adm admin cdrom dialout lpadmin mythtv plugdev sambashare vboxusers
  WifiSyslog: Jul 26 20:23:08 zwei NetworkManager[1174]: <info> Policy set 'Wired connection 2' (eth1) as default for IPv6 routing and DNS.
  _MarkForUpload: True
  dmi.bios.date: 02/04/2009
  dmi.bios.vendor: American Megatrends Inc.
  dmi.bios.version: 0203
  dmi.board.asset.tag: To Be Filled By O.E.M.
  dmi.board.name: P6T DELUXE V2
  dmi.board.vendor: ASUSTeK Computer INC.
  dmi.board.version: Rev 1.xx
  dmi.chassis.asset.tag: Asset-1234567890
  dmi.chassis.type: 3
  dmi.chassis.vendor: Chassis Manufacture
  dmi.chassis.version: Chassis Version
  dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr0203:bd02/04/2009:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKComputerINC.:rnP6TDELUXEV2:rvrRev1.xx:cvnChassisManufacture:ct3:cvrChassisVersion:
  dmi.product.name: System Product Name
  dmi.product.version: System Version
  dmi.sys.vendor: System manufacturer

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