On 6/16/21 4:57 PM, Tejun Heo wrote:

Hello,

On Thu, Jun 03, 2021 at 05:24:14PM -0400, Waiman Long wrote:

quoted

@@ -2181,6 +2192,13 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
  	    (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed)))
  		goto out_unlock;
  
+	/*
+	 * On default hierarchy, task cannot be moved to a cpuset with empty
+	 * effective cpus.
+	 */
+	if (is_in_v2_mode() && cpumask_empty(cs->effective_cpus))
+		goto out_unlock;
+

This is inconsistent with how other events which leave a root partition
empty is handled. Woudln't it be more consistent to switch the parent to
PRS_ERROR and behave accordingly but allow it to have valid child roots?

 From my point of view, PRS_ERROR is used when cpus are gone because of 
cpu hotplug (offline). It can be a temporary condition that will be 
corrected later on. I don't want to use PRS_ERROR for the particular 
case that the users have explicitly distributed out all the cpus to 
child partitions. I will clarify it in the next version and double check 
to make sure that this rule is consistently apply.

Thanks,
Longman