Hi Tejun On Wed, 17 Oct 2018 at 18:20, Tejun Heo <tj@xxxxxxxxxx> wrote: > > Hello, Michael. > > Sorry about the delay. > > On Thu, Oct 04, 2018 at 09:40:57PM +0200, Michael Kerrisk (man-pages) wrote: > > This seems odd. x/y is now of "domain invalid" type with a controller > > enabled! This feels like a violation of the rules, since we can't > > in other circumstances do anything with a "domain invalid" cgroup > > except convert it to "threaded". In particular, we can't create > > child cgroups under a "domain invalid" cgroup, or add member processes > > to the cgroup, or *enable controllers in the cgroup*. In fact, when > > doing the > > > > # echo threaded > x/z/cgroup.type > > > > I had expected a write(2) error because the state of x/y should > > (I thought) not be permitted. > > So, both the interim (before turning x/z into threaded) and final > (after) are completely fine - the cgroups are empty and whether > threaded controllers like pids are enabled or not don't really change > things that much. > > Maybe it is a bit inconsistent to then deny enabling threaded > controllers on invalid domain cgroups. We can lift that restriction > but I personally can't see why that'd be clearly better. So, I also can't see anything that seems harmful in the scenario I described; it's just an odd inconsistency, and I supposed it was unintended/overlooked behavior, and I wanted to alert you to it, in case it seemed problematic. However, as long as you have no concerns, I see no reason to change the existing behavior. Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
