Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups

[Petr Mladek]

On Fri 2016-04-15 10:38:15, Tejun Heo wrote:
> > Anyway, before we go that way, can we at least consider the possibility
> > of removing the kworker creation dependency on the global rwsem? AFAIU
> > this locking was added because of the pid controller. Do we even care
> > about something as volatile as kworkers in the pid controller?
>
> It's not just pid controller and the global percpu locking has lower
> hotpath overhead.  We can try to exclude kworkers out of the locking
> but that can get really nasty and there are already attempts to add
> cgroup support to workqueue.  Will think more about it.

I have played with this idea on Friday. Please, find below a POC.
The worker detection works and the deadlock is removed. But workers
do not appear in the root cgroups. I am not familiar with the cgroups
stuff, so this part is much more difficult for me.

I send it because it might give you an idea when discussing it
on LSF. Please, let me know if I should continue on this way or
if it looks too crazy already now.