[Lxc-users] unmounting cgroup partition

[Serge Hallyn]

Quoting David Shwatrz (dshwatrz at gmail.com):
> Hello,
> 
> When I perform the next sequence it finishes ok:
> mkdir /cgroup/freezer
> mount -t cgroup -o freezer testf /cgroup/freezer/
> umount  /cgroup/freezer
> 
> I had also added printk in the cgroup unmount handler ,
> cgroup_kill_sb(), immediately in the
> beginning of the method, and we reach it (kernel/cgroup.c)
> 
> Now I try the following sequence:
> mkdir /cgroup/freezer
> mount -t cgroup -o freezer testf /cgroup/freezer/
> mkdir /cgroup/freezer/0
> umount  /cgroup/freezer
> 
> We do **not** reach the cgroup_kill_sb()! But there is no error
> message; moreover, mount | grep freezer returns nothing.
> ls -al /cgroup/freezer/ also returns noting
> 
> 
> Now, at this point in running the sequences above, running
> mount -t cgroup -o freezer testf /cgroup/freezer
> and ls /cgroup/freezer
> shows folder "0".
> 
> Now:
> running rmdir /cgroup/freezer/0
> and
> umount /cgroup/freezer
> *does* reach  the cgroup unmount handler , cgroup_kill_sb(),.
> 
> Should we permit unmount if groups still exist under some cgroup topmost root ?

Yes.

-serge