[PATCH 04/17] cgroup/cpuset: Limit type-change accounting to owned CPUs

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

From: Guopeng Zhang <zhangguopeng@kylinos.cn>

effective_xcpus includes CPUs granted to valid child partitions. Passing
the whole mask to isolated_cpus_update() during a root-to-isolated or
isolated-to-root change applies the parent's new state to child-owned
CPUs as well.

Build a mask of CPUs owned by the partition by subtracting the
effective_xcpus of valid children. Use this mask when updating
isolated_cpus for a partition type change.

Fixes: 11e5f407b64a ("cgroup/cpuset: Keep track of CPUs in isolated partitions")
Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
---
 kernel/cgroup/cpuset.c | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 2538faac9aba..468272baadb2 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2155,6 +2155,30 @@ static void compute_partition_effective_cpumask(struct cpuset *cs,
 	rcu_read_unlock();
 }
 
+/*
+ * Compute CPUs owned directly by a partition.
+ *
+ * effective_xcpus includes CPUs granted to valid child partitions. Exclude
+ * those CPUs when changing only this partition's type.
+ */
+static void compute_partition_owned_cpumask(struct cpuset *cs,
+					    struct cpumask *owned_cpus)
+{
+	struct cgroup_subsys_state *css;
+	struct cpuset *child;
+
+	lockdep_assert_held(&cpuset_mutex);
+	cpumask_copy(owned_cpus, cs->effective_xcpus);
+
+	rcu_read_lock();
+	cpuset_for_each_child(child, css, cs) {
+		if (is_partition_valid(child))
+			cpumask_andnot(owned_cpus, owned_cpus,
+				       child->effective_xcpus);
+	}
+	rcu_read_unlock();
+}
+
 /*
  * update_cpumasks_hier - Update effective cpumasks and tasks in the subtree
  * @cs:  the cpuset to consider
@@ -2990,8 +3014,10 @@ 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.
+		 * Need to update isolated_cpus for CPUs owned by this partition,
+		 * excluding CPUs distributed to valid child partitions.
 		 */
+		compute_partition_owned_cpumask(cs, tmpmask.new_cpus);
 		if (((new_prs == PRS_ISOLATED) &&
 		     !isolated_cpus_can_update(cs->effective_xcpus, NULL)) ||
 		    prstate_housekeeping_conflict(new_prs, cs->effective_xcpus))
@@ -3030,7 +3056,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 	if (!is_partition_valid(cs))
 		reset_partition_data(cs);
 	else if (isolcpus_updated)
-		isolated_cpus_update(old_prs, new_prs, cs->effective_xcpus);
+		isolated_cpus_update(old_prs, new_prs, tmpmask.new_cpus);
 	spin_unlock_irq(&callback_lock);
 
 	/* Force update if switching back to member & update effective_xcpus */
-- 
2.43.0