On Tue, Jun 28, 2022 at 04:10:29AM +0900, Tejun Heo <tj@xxxxxxxxxx> wrote: > What I'm trying to say is that cpuset.cpus of child_1 and child_2 are > owned by the parent, Cf On Mon, Jun 13, 2022 at 08:00:56AM -1000, Tejun Heo <tj@xxxxxxxxxx> wrote: > On Mon, Jun 13, 2022 at 07:55:49PM +0200, Michal Koutný wrote: > > I don't think child_*/cpuset.cpus must be owned by root. > > I meant the parent. I'm slightly confused. > so a feature which blocks siblings from intersecting each other > doesn't make whole lot of sense because all those files are under the > control of the parent who would have the power to enable or disable > the restrition anyway. file owner parent/ user (mkdir) `- cpuset.cpus root `- cpuset.cpus.partition root (P) `- child_1/ user ` cpuset.cpus user (*) `- child_2/ user ` cpuset.cpus user (*) The writes to child cpuset.cpus may/may not invalidate parent's (P) partition validity (whether a cpu is left to it to host possible tasks). child_1 vs child_2 overlap affects only whether the children cgroups are a valid partition. I think you mean: writes to children cpuset.cpus should be allowed, possible exclusivity violation should be reported in parent/cpuset.cpus.partition. What I thought was OK: prevent (fail) writes to children cpuset.cpus that'd violate the exclusivity (or would take the last cpu from parent if it's necessary to host a task). IMO, it's similar to failed writes to parent/cgroup.subtree_control in a delegated subtree if the parent still has some tasks (that'd violate internal node constraint). What I think might still be OK: allow writes to children cpuset.cpus that violate exclusivity and report that in children's cpuset.cpus.partition. Writes that'd take last cpu from parent should still fail (similar to the failing subtree_control writes above). Hope that clarifies, Michal
