Re: [PATCH v9 3/7] cgroup/cpuset: Refining features and constraints of a partition

On Sun, Dec 05, 2021 at 01:32:16PM -0500, Waiman Long longman@redhat.com wrote:

@@ -1455,34 +1450,16 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp) switch (parent->partition_root_state) { [...]

• case PRS_ENABLED:
  

• 		if (update_parent_subparts_cpumask(cp, partcmd_update, NULL, tmp))
  

• 			update_tasks_cpumask(parent);
  

• 		update_parent = true;
  

[...]

• if (update_parent) {
  

• 	if (update_parent_subparts_cpumask(cp, partcmd_update, NULL, tmp))
  

• 		update_tasks_cpumask(parent);
  

• 	/*
  

• 	 * The cpuset partition_root_state may be changed
  

• 	 * to PRS_ERROR. Capture it.
  

• 	 */
  

• 	new_prs = cp->partition_root_state;
  

• }
  

IIUC, this ensures that when a parent becomes partition root again, this would propagate downwards to invalidated children.

However, the documentation says:

•   Changing a partition root (valid or invalid) to "member" is
  

•   always allowed.  If there are child partition roots underneath
  

•   it, they will become invalid and unrecoverable.  So care must
  

•   be taken to double check for this condition before disabling
  

•   a partition root.
  

I.e. it suggests a child can be trapped in the unrecoverable state (i.e. not fixable by writing into cpuset.cpus.partition). But this does not happen, right?

Michal