[Bug 1558236] Re: script freezes and eats all CPU, has to be killed, which kills shell and programs inside

[gouri]

Confirmed that bug only happens on Ubuntu 16.04, not on previous Ubuntu
releases and not on Debian 8.3.

Machine has these OSes and can boot any at will, in case it helps:
Debian stable (8.3), Xubuntu 16.04, Xubuntu 15.04, Linux Mint 17.2
(based on Ubuntu 14.04), Fedora 23 XFCE Edition.


** Summary changed:

- script freezes and eats all CPU, has to be killed, which kills shell and programs inside
+ /usr/bin/script freezes and eats all CPU, has to be killed, which kills shell and programs inside

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Title:
  /usr/bin/script freezes and eats all CPU, has to be killed, which
  kills shell and programs inside

Status in util-linux package in Ubuntu:
  New

Bug description:
  # Context

  I've been using /usr/bin/script quite a lot for about 4 years (since
  about Ubuntu 12.04, maybe before). It always worked without problem.

  I'm using several script instance most of the time, in several
  terminals.

  Reproducible: randomly, once every few days.

  Problem happens since Ubuntu 16.04. Never seen before (12.04 12.10
  13.04 13.10 14.04 14.10 15.04 15.10).

  # Expected

  Continued operation, terminal running programs normally, little CPU
  used.

  # Observed

  Suddenly, terminal freezes. 
  Other tabs of same terminal window not affected.
  Top shows script consumes 100% CPU.

  Strace shows an endless stream of this line:

  poll([{fd=4, events=POLLIN}], 1, 10)    = 1 ([{fd=4, revents=POLLIN}])

  /proc/*/fd shows what file descriptor it is:

  total 0
  dr-x------ 2 stephane stephane  0 mars  16 20:03 .
  dr-xr-xr-x 9 stephane stephane  0 mars  16 20:03 ..
  lrwx------ 1 stephane stephane 64 mars  16 20:15 0 -> /dev/pts/17 (deleted)
  lrwx------ 1 stephane stephane 64 mars  16 20:15 1 -> /dev/pts/17 (deleted)
  lrwx------ 1 stephane stephane 64 mars  16 20:03 2 -> /dev/pts/17 (deleted)
  lrwx------ 1 stephane stephane 64 mars  16 20:15 3 -> /dev/ptmx
  lrwx------ 1 stephane stephane 64 mars  16 20:15 4 -> /dev/pts/21
  lrwx------ 1 stephane stephane 64 mars  16 20:15 5 -> anon_inode:[signalfd]
  l-wx------ 1 stephane stephane 64 mars  16 20:15 6 -> /somewhere/mylogfile.txt
  l-wx------ 1 stephane stephane 64 mars  16 20:15 7 -> /somewhere/mylogfile_timings.txt

  What can we do?

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: bsdutils 1:2.27.1-6ubuntu1
  ProcVersionSignature: Ubuntu 4.4.0-13.29-generic 4.4.5
  Uname: Linux 4.4.0-13-generic x86_64
  ApportVersion: 2.20-0ubuntu3
  Architecture: amd64
  CurrentDesktop: XFCE
  Date: Wed Mar 16 20:04:02 2016
  ExecutablePath: /usr/bin/script
  InstallationDate: Installed on 2016-02-03 (41 days ago)
  InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160203)
  SourcePackage: util-linux
  UpgradeStatus: No upgrade log present (probably fresh install)

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