[PATCH REPOST RFC cgroup/for-3.7] cgroup: mark subsystems with broken hierarchy support and whine if cgroups are nested for them

[Li Zefan]

On 2012/9/11 6:33, Tejun Heo wrote:
> (forgot cc'ing containers / cgroups mailing lists and used the old
>  address for Li.  Reposting.  Sorry for the noise.)
> 
> Currently, cgroup hierarchy support is a mess.  cpu related subsystems
> behave correctly - configuration, accounting and control on a parent
> properly cover its children.  blkio and freezer completely ignore
> hierarchy and treat all cgroups as if they're directly under the root
> cgroup.  Others show yet different behaviors.
> 
> These differing interpretations of cgroup hierarchy make using cgroup
> confusing and it impossible to co-mount controllers into the same
> hierarchy and obtain sane behavior.
> 
> Eventually, we want full hierarchy support from all subsystems and
> probably a unified hierarchy.  Users using separate hierarchies
> expecting completely different behaviors depending on the mounted
> subsystem is deterimental to making any progress on this front.
> 
> This patch adds cgroup_subsys.broken_hierarchy and sets it to %true
> for controllers which are lacking in hierarchy support.  The goal of
> this patch is two-fold.
> 
> * Move users away from using hierarchy on currently non-hierarchical
>   subsystems, so that implementing proper hierarchy support on those
>   doesn't surprise them.
> 
> * Keep track of which controllers are broken how and nudge the
>   subsystems to implement proper hierarchy support.
> 
> For now, start with a single warning message.  We can whine louder
> later on.
> 
> (I tried to document what's broken and how it should be fixed.  If I
>  got something wrong, please let me know.)
> 

So isn't cpuset broken too? child cpuset's cpu mask isn't necessary a subset
of the parent's if the cpu_exclusive flag is not set.