cgroup/cpuset: Code cleanup and comment update

Rename partition_xcpus_newstate() to isolated_cpus_update(),
update_partition_exclusive() to update_partition_exclusive_flag() and
the new_xcpus_state variable to isolcpus_updated to make their meanings
more explicit. Also add some comments to further clarify the code.
No functional change is expected.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: Waiman-Long

kernel/cgroup/cpuset.c

@@ -65,7 +65,13 @@ static const char * const perr_strings[] = {
 };
 
 /*
- * Exclusive CPUs distributed out to sub-partitions of top_cpuset
+ * For local partitions, update to subpartitions_cpus & isolated_cpus is done
+ * in update_parent_effective_cpumask(). For remote partitions, it is done in
+ * the remote_partition_*() and remote_cpus_update() helpers.
+ */
+/*
+ * Exclusive CPUs distributed out to local or remote sub-partitions of
+ * top_cpuset
  */
 static cpumask_var_t	subpartitions_cpus;
 
@@ -1089,9 +1095,14 @@ void cpuset_reset_sched_domains(void)
  *
  * Iterate through each task of @cs updating its cpus_allowed to the
  * effective cpuset's.  As this function is called with cpuset_mutex held,
- * cpuset membership stays stable. For top_cpuset, task_cpu_possible_mask()
- * is used instead of effective_cpus to make sure all offline CPUs are also
- * included as hotplug code won't update cpumasks for tasks in top_cpuset.
+ * cpuset membership stays stable.
+ *
+ * For top_cpuset, task_cpu_possible_mask() is used instead of effective_cpus
+ * to make sure all offline CPUs are also included as hotplug code won't
+ * update cpumasks for tasks in top_cpuset.
+ *
+ * As task_cpu_possible_mask() can be task dependent in arm64, we have to
+ * do cpu masking per task instead of doing it once for all.
  */
 void cpuset_update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus)
 {
@@ -1151,7 +1162,7 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
  *
  * Return: 0 if successful, an error code otherwise
  */
-static int update_partition_exclusive(struct cpuset *cs, int new_prs)
+static int update_partition_exclusive_flag(struct cpuset *cs, int new_prs)
 {
 	bool exclusive = (new_prs > PRS_MEMBER);
 
@@ -1234,12 +1245,12 @@ static void reset_partition_data(struct cpuset *cs)
 }
 
 /*
- * partition_xcpus_newstate - Exclusive CPUs state change
+ * isolated_cpus_update - Update the isolated_cpus mask
  * @old_prs: old partition_root_state
  * @new_prs: new partition_root_state
  * @xcpus: exclusive CPUs with state change
  */
-static void partition_xcpus_newstate(int old_prs, int new_prs, struct cpumask *xcpus)
+static void isolated_cpus_update(int old_prs, int new_prs, struct cpumask *xcpus)
 {
 	WARN_ON_ONCE(old_prs == new_prs);
 	if (new_prs == PRS_ISOLATED)
@@ -1273,8 +1284,8 @@ static bool partition_xcpus_add(int new_prs, struct cpuset *parent,
 
 	isolcpus_updated = (new_prs != parent->partition_root_state);
 	if (isolcpus_updated)
-		partition_xcpus_newstate(parent->partition_root_state, new_prs,
-					 xcpus);
+		isolated_cpus_update(parent->partition_root_state, new_prs,
+				     xcpus);
 
 	cpumask_andnot(parent->effective_cpus, parent->effective_cpus, xcpus);
 	return isolcpus_updated;
@@ -1304,8 +1315,8 @@ static bool partition_xcpus_del(int old_prs, struct cpuset *parent,
 
 	isolcpus_updated = (old_prs != parent->partition_root_state);
 	if (isolcpus_updated)
-		partition_xcpus_newstate(old_prs, parent->partition_root_state,
-					 xcpus);
+		isolated_cpus_update(old_prs, parent->partition_root_state,
+				     xcpus);
 
 	cpumask_and(xcpus, xcpus, cpu_active_mask);
 	cpumask_or(parent->effective_cpus, parent->effective_cpus, xcpus);
@@ -1634,8 +1645,8 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 	int old_prs, new_prs;
 	int part_error = PERR_NONE;	/* Partition error? */
 	int subparts_delta = 0;
-	struct cpumask *xcpus;		/* cs effective_xcpus */
 	int isolcpus_updated = 0;
+	struct cpumask *xcpus = user_xcpus(cs);
 	bool nocpu;
 
 	lockdep_assert_held(&cpuset_mutex);
@@ -1647,7 +1658,6 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 	 */
 	adding = deleting = false;
 	old_prs = new_prs = cs->partition_root_state;
-	xcpus = user_xcpus(cs);
 
 	if (cmd == partcmd_invalidate) {
 		if (is_prs_invalid(old_prs))
@@ -1861,7 +1871,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 	 * CPU lists in cs haven't been updated yet. So defer it to later.
 	 */
 	if ((old_prs != new_prs) && (cmd != partcmd_update))  {
-		int err = update_partition_exclusive(cs, new_prs);
+		int err = update_partition_exclusive_flag(cs, new_prs);
 
 		if (err)
 			return err;
@@ -1899,7 +1909,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 	update_unbound_workqueue_cpumask(isolcpus_updated);
 
 	if ((old_prs != new_prs) && (cmd == partcmd_update))
-		update_partition_exclusive(cs, new_prs);
+		update_partition_exclusive_flag(cs, new_prs);
 
 	if (adding || deleting) {
 		cpuset_update_tasks_cpumask(parent, tmp->addmask);
@@ -2829,7 +2839,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 	int err = PERR_NONE, old_prs = cs->partition_root_state;
 	struct cpuset *parent = parent_cs(cs);
 	struct tmpmasks tmpmask;
-	bool new_xcpus_state = false;
+	bool isolcpus_updated = false;
 
 	if (old_prs == new_prs)
 		return 0;
@@ -2843,7 +2853,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 	if (alloc_cpumasks(NULL, &tmpmask))
 		return -ENOMEM;
 
-	err = update_partition_exclusive(cs, new_prs);
+	err = update_partition_exclusive_flag(cs, new_prs);
 	if (err)
 		goto out;
 
@@ -2884,8 +2894,9 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 	} else if (old_prs && new_prs) {
 		/*
 		 * A change in load balance state only, no change in cpumasks.
+		 * Need to update isolated_cpus.
 		 */
-		new_xcpus_state = true;
+		isolcpus_updated = true;
 	} else {
 		/*
 		 * Switching back to member is always allowed even if it
@@ -2909,22 +2920,26 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 	 */
 	if (err) {
 		new_prs = -new_prs;
-		update_partition_exclusive(cs, new_prs);
+		update_partition_exclusive_flag(cs, new_prs);
 	}
 
 	spin_lock_irq(&callback_lock);
 	cs->partition_root_state = new_prs;
 	WRITE_ONCE(cs->prs_err, err);
 	if (!is_partition_valid(cs))
 		reset_partition_data(cs);
-	else if (new_xcpus_state)
-		partition_xcpus_newstate(old_prs, new_prs, cs->effective_xcpus);
+	else if (isolcpus_updated)
+		isolated_cpus_update(old_prs, new_prs, cs->effective_xcpus);
 	spin_unlock_irq(&callback_lock);
-	update_unbound_workqueue_cpumask(new_xcpus_state);
+	update_unbound_workqueue_cpumask(isolcpus_updated);
 
-	/* Force update if switching back to member */
+	/* Force update if switching back to member & update effective_xcpus */
 	update_cpumasks_hier(cs, &tmpmask, !new_prs);
 
+	/* A newly created partition must have effective_xcpus set */
+	WARN_ON_ONCE(!old_prs && (new_prs > 0)
+			      && cpumask_empty(cs->effective_xcpus));
+
 	/* Update sched domains and load balance flag */
 	update_partition_sd_lb(cs, old_prs);