[lxc-users] Strange CPUSET CGROUP behaviour

[Christian Brauner]

On Thu, Sep 03, 2020 at 03:27:37PM +0100, Ben Green wrote:
> Hi all,
> 
> We are starting to use LXC in production here, after solving our final
> problem (inconsistent and disappearing cgroup space - Thread name
> "Disappearing Cgroups" on this list) completely with the help of Serge
> E. Hallyn.
> 
> Now something odd has come up. I have one server on the Debian kernel
> 4.19.0-9-amd64 and another on 4.19.0-10-amd64. On the 4.19.0-9-amd64
> kernel we cat this:
> 
> # cat /sys/fs/cgroup/cpuset/forcontainers/tasks
> 1216
> 5065
> 12372
> etc.
> 
> But on the other one with the 4.19.0-10-amd64 we get this:
> 
> #  cat /sys/fs/cgroup/cpuset/forcontainers/tasks
> 
> No output! Also on the 4.19.0-10-amd64 machine it is not possible to add
> to the list of tasks:
> 
> # echo $$ >> /sys/fs/cgroup/cpuset/forcontainers/tasks
> -bash: echo: write error: No space left on device

That usually indicates that cpuset.cpus and/or cpuset.mems is empty and
that cgroup.clone_children in the parent cgroup isn't set to 1. LXC
should usually take care of this though.

Christian