[PATCH v4 1/7] cgroup/cpuset: Factor out child partition validation

[Guopeng Zhang <guopeng.zhang@linux.dev>]

From: Guopeng Zhang <zhangguopeng@kylinos.cn>

compute_partition_effective_cpumask() checks whether each valid child
partition remains covered by the parent exclusive CPU mask and whether it
would consume all remaining active CPUs of a populated parent.

Factor these two checks into cs_partition_error() so the same rules can be
reused when evaluating a proposed parent configuration. This is a
preparatory refactoring with no intended functional change.

Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
---
 kernel/cgroup/cpuset.c | 47 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 38 insertions(+), 9 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 8f24171b6055..a2514fcb1144 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2085,6 +2085,37 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 	return 0;
 }
 
+/**
+ * cs_partition_error - Return a cpuset partition invalidation error
+ * @cs: Partition being evaluated
+ * @parent_xcpus: Parent's complete effective exclusive CPU mask, including
+ *                offline CPUs
+ * @remaining_ecpus: Parent's active effective CPUs remaining before @cs is
+ *                   evaluated
+ * @parent_populated: Whether the parent partition contains tasks
+ *
+ * @remaining_ecpus may still contain active CPUs assigned to @cs and to
+ * children that have not yet been evaluated. It excludes only CPUs assigned
+ * to previously evaluated children that remain valid.
+ *
+ * Return: The error that would invalidate @cs, or PERR_NONE
+ */
+static enum prs_errcode
+cs_partition_error(struct cpuset *cs,
+		   const struct cpumask *parent_xcpus,
+		   const struct cpumask *remaining_ecpus,
+		   bool parent_populated)
+{
+	if (!cpumask_subset(cs->effective_xcpus, parent_xcpus))
+		return PERR_INVCPUS;
+
+	if (parent_populated &&
+	    cpumask_subset(remaining_ecpus, cs->effective_xcpus))
+		return PERR_NOCPUS;
+
+	return PERR_NONE;
+}
+
 /**
  * compute_partition_effective_cpumask - compute effective_cpus for partition
  * @cs: partition root cpuset
@@ -2121,6 +2152,8 @@ static void compute_partition_effective_cpumask(struct cpuset *cs,
 
 	rcu_read_lock();
 	cpuset_for_each_child(child, css, cs) {
+		enum prs_errcode child_err;
+
 		if (!is_partition_valid(child))
 			continue;
 
@@ -2129,15 +2162,11 @@ static void compute_partition_effective_cpumask(struct cpuset *cs,
 		 * partition root.
 		 */
 		WARN_ON_ONCE(is_remote_partition(child));
-		WRITE_ONCE(child->prs_err, 0);
-		if (!cpumask_subset(child->effective_xcpus,
-				    cs->effective_xcpus))
-			WRITE_ONCE(child->prs_err, PERR_INVCPUS);
-		else if (populated &&
-			 cpumask_subset(new_ecpus, child->effective_xcpus))
-			WRITE_ONCE(child->prs_err, PERR_NOCPUS);
-
-		if (child->prs_err) {
+		child_err = cs_partition_error(child, cs->effective_xcpus,
+					       new_ecpus, populated);
+		WRITE_ONCE(child->prs_err, child_err);
+
+		if (child_err) {
 			int old_prs = child->partition_root_state;
 
 			/*
-- 
2.43.0