linux-kernel - [PATCH -next RFC 05/16] cpuset: factor out partition

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Message-Id: <20250928071306.3797436-6-chenridong@huaweicloud.com>
Date: Sun, 28 Sep 2025 07:12:55 +0000
From: Chen Ridong <chenridong@...weicloud.com>
To: longman@...hat.com,
	tj@...nel.org,
	hannes@...xchg.org,
	mkoutny@...e.com
Cc: cgups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lujialin4@...wei.com,
	chenridong@...wei.com
Subject: [PATCH -next RFC 05/16] cpuset: factor out partition_update() function

From: Chen Ridong <chenridong@...wei.com>

Extract the core partition update logic into a dedicated partition_update()
function. This refactoring centralizes updates to key cpuset data
structures including remote_sibling, effective_xcpus, partition_root_state,
and prs_err.

The function handles the complete partition update workflow:
- Adding and removing exclusive CPUs via partition_xcpus_add()/del()
- Managing remote sibling relationships
- Synchronizing effective exclusive CPUs mask
- Updating partition state and error status
- Triggering required system updates and workqueue synchronization

This creates a coherent interface for partition operations and establishes
a foundation for enhanced partition management while maintaining existing
remote partition behavior.

Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 kernel/cgroup/cpuset.c | 71 ++++++++++++++++++++++++++++--------------
 1 file changed, 47 insertions(+), 24 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 1944410ae872..0e2f95daf459 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1587,6 +1587,49 @@ static void partition_disable(struct cpuset *cs, struct cpuset *parent,
 	cpuset_force_rebuild();
 }
 
+/**
+ * partition_update - Update an existing partition configuration
+ * @cs: The cpuset to update
+ * @prs: Partition root state (must be positive)
+ * @xcpus: New exclusive CPUs mask for the partition (NULL to keep current)
+ * @excpus: New effective exclusive CPUs mask
+ * @tmp: Temporary masks
+ *
+ * Updates partition-related fields. The tmp->addmask is the CPU mask that
+ * will be added to the subpartitions_cpus and removed from parent's
+ * effective_cpus, and the tmp->delmask vice versa.
+ */
+static void partition_update(struct cpuset *cs, int prs, struct cpumask *xcpus,
+				  struct cpumask *excpus, struct tmpmasks *tmp)
+{
+	bool isolcpus_updated;
+	bool excl_updated;
+	struct cpuset *parent;
+
+	lockdep_assert_held(&cpuset_mutex);
+	WARN_ON_ONCE(!cpuset_v2());
+	WARN_ON_ONCE(prs <= 0);
+
+	parent = is_remote_partition(cs) ? NULL : parent_cs(cs);
+	excl_updated = !cpumask_empty(tmp->addmask) ||
+			!cpumask_empty(tmp->delmask);
+
+	spin_lock_irq(&callback_lock);
+	isolcpus_updated = partition_xcpus_add(prs, parent, tmp->addmask);
+	isolcpus_updated |= partition_xcpus_del(prs, parent, tmp->delmask);
+	/*
+	 * Need to update effective_xcpus and exclusive_cpus now as
+	 * update_sibling_cpumasks() below may iterate back to the same cs.
+	 */
+	cpumask_copy(cs->effective_xcpus, excpus);
+	if (xcpus)
+		cpumask_copy(cs->exclusive_cpus, xcpus);
+	spin_unlock_irq(&callback_lock);
+	update_unbound_workqueue_cpumask(isolcpus_updated);
+	if (excl_updated)
+		cpuset_force_rebuild();
+}
+
 /*
  * remote_partition_enable - Enable current cpuset as a remote partition root
  * @cs: the cpuset to update
@@ -1669,10 +1712,6 @@ static void remote_partition_disable(struct cpuset *cs, struct tmpmasks *tmp)
 static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
 			       struct cpumask *excpus, struct tmpmasks *tmp)
 {
-	bool adding, deleting;
-	int prs = cs->partition_root_state;
-	int isolcpus_updated = 0;
-
 	if (WARN_ON_ONCE(!is_remote_partition(cs)))
 		return;
 
@@ -1683,15 +1722,15 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
 		goto invalidate;
 	}
 
-	adding   = cpumask_andnot(tmp->addmask, excpus, cs->effective_xcpus);
-	deleting = cpumask_andnot(tmp->delmask, cs->effective_xcpus, excpus);
+	cpumask_andnot(tmp->addmask, excpus, cs->effective_xcpus);
+	cpumask_andnot(tmp->delmask, cs->effective_xcpus, excpus);
 
 	/*
 	 * Additions of remote CPUs is only allowed if those CPUs are
 	 * not allocated to other partitions and there are effective_cpus
 	 * left in the top cpuset.
 	 */
-	if (adding) {
+	if (!cpumask_empty(tmp->addmask)) {
 		WARN_ON_ONCE(cpumask_intersects(tmp->addmask, subpartitions_cpus));
 		if (!capable(CAP_SYS_ADMIN))
 			cs->prs_err = PERR_ACCESS;
@@ -1702,23 +1741,7 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
 			goto invalidate;
 	}
 
-	spin_lock_irq(&callback_lock);
-	if (adding)
-		isolcpus_updated += partition_xcpus_add(prs, NULL, tmp->addmask);
-	if (deleting)
-		isolcpus_updated += partition_xcpus_del(prs, NULL, tmp->delmask);
-	/*
-	 * Need to update effective_xcpus and exclusive_cpus now as
-	 * update_sibling_cpumasks() below may iterate back to the same cs.
-	 */
-	cpumask_copy(cs->effective_xcpus, excpus);
-	if (xcpus)
-		cpumask_copy(cs->exclusive_cpus, xcpus);
-	spin_unlock_irq(&callback_lock);
-	update_unbound_workqueue_cpumask(isolcpus_updated);
-	if (adding || deleting)
-		cpuset_force_rebuild();
-
+	partition_update(cs, cs->partition_root_state, xcpus, excpus, tmp);
 	/*
 	 * Propagate changes in top_cpuset's effective_cpus down the hierarchy.
 	 */
-- 
2.34.1