Bug#803013: systemd should not destroy application created cgroups

[paul.szabo at sydney.edu.au]

Dear Martin,

>>   # Set things up
>>   mkdir /sys/fs/cgroup/cpu/mytest
>>   echo $$ > /sys/fs/cgroup/cpu/mytest/tasks
>>   # Check it is there
>>   grep . /sys/fs/cgroup/cpu/mytest/tasks
>>   # Do the systemd thing
>>   systemctl daemon-reload
>>   systemctl start anacron
>>   # See it gone
>>   grep . /sys/fs/cgroup/cpu/mytest/tasks
>
> FTR, I was testing this in a jessie VM now, and I can't reproduce the
> cgroup changes there either. So this is more subtle to reproduce.

Thanks for testing. However, the test "works" for me on jessie:

root at p639:~# COLUMNS=120 dpkg -l | grep systemd
ii  libpam-systemd:amd64     215-17+deb8u2     amd64             system and service manager - PAM module
ii  libsystemd-daemon0:amd64 215-17+deb8u2     amd64             systemd utility library (deprecated)
ii  libsystemd-login0:amd64  215-17+deb8u2     amd64             systemd login utility library (deprecated)
ii  libsystemd0:amd64        215-17+deb8u2     amd64             systemd utility library
ii  systemd                  215-17+deb8u2     amd64             system and service manager
ii  systemd-sysv             215-17+deb8u2     amd64             system and service manager - SysV links
root at p639:~# mkdir /sys/fs/cgroup/cpu/mytest
mkdir: cannot create directory ?/sys/fs/cgroup/cpu/mytest?: File exists
root at p639:~# grep .  /sys/fs/cgroup/cpu/mytest/tasks
root at p639:~# echo $$ > /sys/fs/cgroup/cpu/mytest/tasks
root at p639:~# grep .  /sys/fs/cgroup/cpu/mytest/tasks
7198
root at p639:~# systemctl daemon-reload
root at p639:~# systemctl start anacron
root at p639:~# grep .  /sys/fs/cgroup/cpu/mytest/tasks
root at p639:~# 

and the issue is fixed with my patch:

root at p639:~# COLUMNS=120 dpkg -l | grep systemd
ii  libpam-systemd:amd64     215-17+deb8u2.psz amd64             system and service manager - PAM module
ii  libsystemd-daemon0:amd64 215-17+deb8u2     amd64             systemd utility library (deprecated)
ii  libsystemd-login0:amd64  215-17+deb8u2     amd64             systemd login utility library (deprecated)
ii  libsystemd0:amd64        215-17+deb8u2.psz amd64             systemd utility library
ii  systemd                  215-17+deb8u2.psz amd64             system and service manager
ii  systemd-sysv             215-17+deb8u2.psz amd64             system and service manager - SysV links
root at p639:~# grep .  /sys/fs/cgroup/cpu/mytest/tasks
root at p639:~# echo $$ > /sys/fs/cgroup/cpu/mytest/tasks
root at p639:~# grep .  /sys/fs/cgroup/cpu/mytest/tasks
7198
root at p639:~# systemctl daemon-reload
root at p639:~# systemctl start anacron
root at p639:~# grep .  /sys/fs/cgroup/cpu/mytest/tasks
7198
root at p639:~# 

I wonder what is different between your jessie machine and mine.

Cheers, Paul

Paul Szabo   psz at maths.usyd.edu.au   http://www.maths.usyd.edu.au/u/psz/
School of Mathematics and Statistics   University of Sydney    Australia