cpuset: update cpuset->effective_{cpus,mems} at hotplug

We're going to have separate user-configured masks and effective ones.

Eventually configured masks can only be changed by writing cpuset.cpus
and cpuset.mems, and they won't be restricted by parent cpuset. While
effective masks reflect cpu/memory hotplug and hierachical restriction,
and these are the real masks that apply to the tasks in the cpuset.

We calculate effective mask this way:
  - top cpuset's effective_mask == online_mask, otherwise
  - cpuset's effective_mask == configured_mask & parent effective_mask,
    if the result is empty, it inherits parent effective mask.

Those behavior changes are for default hierarchy only. For legacy
hierarchy, effective_mask and configured_mask are the same, so we won't
break old interfaces.

To make cs->effective_{cpus,mems} to be effective masks, we need to
  - update the effective masks at hotplug
  - update the effective masks at config change
  - take on ancestor's mask when the effective mask is empty

The first item is done here.

This won't introduce behavior change.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cpuset.c

@@ -2082,6 +2082,7 @@ retry:
 
 	mutex_lock(&callback_mutex);
 	cpumask_andnot(cs->cpus_allowed, cs->cpus_allowed, &off_cpus);
+	cpumask_andnot(cs->effective_cpus, cs->effective_cpus, &off_cpus);
 	mutex_unlock(&callback_mutex);
 
 	/*
@@ -2096,6 +2097,7 @@ retry:
 
 	mutex_lock(&callback_mutex);
 	nodes_andnot(cs->mems_allowed, cs->mems_allowed, off_mems);
+	nodes_andnot(cs->effective_mems, cs->effective_mems, off_mems);
 	mutex_unlock(&callback_mutex);
 
 	/*
@@ -2159,6 +2161,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
 	if (cpus_updated) {
 		mutex_lock(&callback_mutex);
 		cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
+		cpumask_copy(top_cpuset.effective_cpus, &new_cpus);
 		mutex_unlock(&callback_mutex);
 		/* we don't mess with cpumasks of tasks in top_cpuset */
 	}
@@ -2167,6 +2170,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
 	if (mems_updated) {
 		mutex_lock(&callback_mutex);
 		top_cpuset.mems_allowed = new_mems;
+		top_cpuset.effective_mems = new_mems;
 		mutex_unlock(&callback_mutex);
 		update_tasks_nodemask(&top_cpuset);
 	}