[Lxc-users] dangling cgroups after lxc-execute with ns_cgroup

[Serge Hallyn]

Quoting Arun M (arunmahadevaiyer at gmail.com):
> Hi,
> 
> I updated to lxc-0.8.0-rc2 and after that I observe dangling cgroups
> (/cgroup/PID) in the filesystem after lxc-execute terminates.
> 
> I am using ns_cgroup.

Which kernel are you on?  The ns cgroup is no longer available since
over a year ago.

> Looks like a process is spawned in a new namespace but lxc-fails to remove
> the cgroup directory.

Can you show 'ps -ef'?   If you can identify the process that won't
die, can you see what it's doing (strace -f -o outfile -p $pid) ?

My only guess would be that the container_reboot_supported() function,
which gets cloned, is for some reason not dying.  Except no, that
can't be it, because this change actually moves that clone() to the
monitor task, so it wouldn't be pinning the cgroup.

Can you check whether your container is mounting a private /var or
/run?  My theory is that the initial task is never killed because you
are relying on the utmp watcher (being on an older kernel), and the
container is using a utmp that the monitor can't see.

> After a long time these dangling cgroups collide with new PIDs and
> lxc-execute fails with "File exists".
> 
> Apparently caused due to commit -
> http://lxc.git.sourceforge.net/git/gitweb.cgi?p=lxc/lxc;a=commit;h=69182a318c3ba35f56a88891cabad25d9f7985b6
> 
> This problem does not happen if I go to an earlier revision.
> 
> Thanks,
> Arun