linux-kernel - [PATCH -next RFC 03/16] cpuset: factor out partition

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Message-Id: <20250928071306.3797436-4-chenridong@huaweicloud.com>
Date: Sun, 28 Sep 2025 07:12:53 +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 03/16] cpuset: factor out partition_enable() function

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

Extract the core partition enablement logic into a dedicated
partition_enable() 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 enablement workflow:
- Adding exclusive CPUs via partition_xcpus_add()
- Managing remote sibling relationships
- Synchronizing effective exclusive CPUs mask
- Updating partition state and error status
- Triggering required scheduler domain rebuilds

This creates a coherent interface for partition operations and establishes
a foundation for future local partition support while maintaining existing
remote partition behavior.

Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 kernel/cgroup/cpuset.c | 55 +++++++++++++++++++++++++++++++++---------
 1 file changed, 44 insertions(+), 11 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 0787904321a9..43ce62f4959c 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1515,6 +1515,49 @@ static inline bool is_local_partition(struct cpuset *cs)
 	return is_partition_valid(cs) && !is_remote_partition(cs);
 }
 
+static void partition_state_update(struct cpuset *cs, int new_prs,
+					  enum prs_errcode prs_err)
+{
+	lockdep_assert_held(&callback_lock);
+
+	cs->partition_root_state = new_prs;
+	WRITE_ONCE(cs->prs_err, prs_err);
+	if (!is_partition_valid(cs))
+		reset_partition_data(cs);
+}
+
+/**
+ * partition_enable - Transitions a cpuset to a partition root
+ * @cs: The cpuset to enable partition for
+ * @parent: Parent cpuset of @cs, NULL for remote parent
+ * @new_prs: New partition root state to set
+ * @new_excpus: New exclusive CPUs mask for the partition
+ *
+ * Transitions a cpuset to a partition root, only for v2.
+ */
+static void partition_enable(struct cpuset *cs, struct cpuset *parent,
+				 int new_prs, struct cpumask *new_excpus)
+{
+	bool isolcpus_updated;
+
+	lockdep_assert_held(&cpuset_mutex);
+	WARN_ON_ONCE(new_prs <= 0);
+	WARN_ON_ONCE(!cpuset_v2());
+
+	if (cs->partition_root_state == new_prs)
+		return;
+
+	spin_lock_irq(&callback_lock);
+	/* enable partition should only add exclusive cpus */
+	isolcpus_updated = partition_xcpus_add(new_prs, parent, new_excpus);
+	list_add(&cs->remote_sibling, &remote_children);
+	cpumask_copy(cs->effective_xcpus, new_excpus);
+	partition_state_update(cs, new_prs, PERR_NONE);
+	spin_unlock_irq(&callback_lock);
+	update_unbound_workqueue_cpumask(isolcpus_updated);
+	cpuset_force_rebuild();
+}
+
 /*
  * remote_partition_enable - Enable current cpuset as a remote partition root
  * @cs: the cpuset to update
@@ -1528,8 +1571,6 @@ static inline bool is_local_partition(struct cpuset *cs)
 static int remote_partition_enable(struct cpuset *cs, int new_prs,
 				   struct tmpmasks *tmp)
 {
-	bool isolcpus_updated;
-
 	/*
 	 * The user must have sysadmin privilege.
 	 */
@@ -1552,15 +1593,7 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
 	    cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus))
 		return PERR_INVCPUS;
 
-	spin_lock_irq(&callback_lock);
-	isolcpus_updated = partition_xcpus_add(new_prs, NULL, tmp->new_cpus);
-	list_add(&cs->remote_sibling, &remote_children);
-	cpumask_copy(cs->effective_xcpus, tmp->new_cpus);
-	spin_unlock_irq(&callback_lock);
-	update_unbound_workqueue_cpumask(isolcpus_updated);
-	cpuset_force_rebuild();
-	cs->prs_err = 0;
-
+	partition_enable(cs, NULL, new_prs, tmp->new_cpus);
 	/*
 	 * Propagate changes in top_cpuset's effective_cpus down the hierarchy.
 	 */
-- 
2.34.1