[Bug 1553353] Re: tail'ing a file in a script session hangs

[Simon Déziel]

After bisecting util-linux, the problematic commit is:

54c6611d6f7b73609a5331f4d0bcf63c4af6429e is the first bad commit
commit 54c6611d6f7b73609a5331f4d0bcf63c4af6429e
Author: Karel Zak <kzak at redhat.com>
Date:   Wed Jun 17 15:48:50 2015 +0200

    script: fix EOF problems
    
    * remove STDIN from poll() if:
    
      * STDIN already closed -- poll returns POLLHUP, for example:
    
    		echo "date" | script
    
      * detect EOF as returned by read(), for example:
    
    		script -c "echo Hello" < /dev/null
    
    * don't write to master when there is still something to read from
      slave (it means shell is not initialized yet or busy)
    
    Signed-off-by: Karel Zak <kzak at redhat.com>

:040000 040000 2cc2b7f5d69f16775151517912dce6ff3a586847
b1a8465b2c3f23c0f41bfb7308af49b92963e77b M      term-utils


When using v2.27.1 and reverting just this commit, all is fine.

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https://bugs.launchpad.net/bugs/1553353

Title:
  tail'ing a file in a script session hangs

Status in util-linux package in Ubuntu:
  Confirmed
Status in util-linux source package in Xenial:
  Confirmed

Bug description:
  Steps to reproduce:

  1) Start script session (same issue when script is saving to /dev/null)
  script # or: script /dev/null
  2) Tail a file
  tail -f /var/log/syslog
  3) Press "Enter" 2 times
  4) Notice the script process taking 100% CPU

  This regression is rather new but I don't know which update introduced
  it. Reverting util-linux/bsdutils to the previous version doesn't help
  so maybe it's not even script's fault. tail/coreutils hasn't been
  update in a long time so I'm not sure who's fault it is. I can
  reproduce the problem with kernel 4.4.0-9-generic and
  4.4.0-10-generic.


  $ lsb_release -rd
  Description:	Ubuntu Xenial Xerus (development branch)
  Release:	16.04

  $ apt-cache policy util-linux bsdutils coreutils
  util-linux:
    Installed: 2.27.1-4ubuntu1
    Candidate: 2.27.1-4ubuntu1
    Version table:
   *** 2.27.1-4ubuntu1 500
          500 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages
          100 /var/lib/dpkg/status
       2.27.1-3ubuntu1 500
          500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages
  bsdutils:
    Installed: 1:2.27.1-4ubuntu1
    Candidate: 1:2.27.1-4ubuntu1
    Version table:
   *** 1:2.27.1-4ubuntu1 500
          500 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages
          100 /var/lib/dpkg/status
       1:2.27.1-3ubuntu1 500
          500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages
  coreutils:
    Installed: 8.25-2ubuntu2
    Candidate: 8.25-2ubuntu2
    Version table:
   *** 8.25-2ubuntu2 500
          500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages
          100 /var/lib/dpkg/status

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: util-linux 2.27.1-4ubuntu1
  ProcVersionSignature: Ubuntu 4.4.0-10.25-generic 4.4.3
  Uname: Linux 4.4.0-10-generic x86_64
  NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
  ApportVersion: 2.20-0ubuntu3
  Architecture: amd64
  CurrentDesktop: Unity
  Date: Fri Mar  4 15:14:15 2016
  SourcePackage: util-linux
  UpgradeStatus: No upgrade log present (probably fresh install)

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