linux-kernel - [PATCH -next 09/11] cpuset: introduce partition_cpus

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Message-Id: <20250917060454.2885698-10-chenridong@huaweicloud.com>
Date: Wed, 17 Sep 2025 06:04:52 +0000
From: Chen Ridong <chenridong@...weicloud.com>
To: longman@...hat.com,
	tj@...nel.org,
	hannes@...xchg.org,
	mkoutny@...e.com
Cc: cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lujialin4@...wei.com,
	chenridong@...wei.com
Subject: [PATCH -next 09/11] cpuset: introduce partition_cpus_change

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

Introduce the partition_cpus_change function to handle both regular CPU
set updates and exclusive CPU modifications, either of which may trigger
partition state changes. This generalized function will also be utilized
for exclusive CPU updates in subsequent patches.

With the introduction of compute_trialcs_excpus in a previous patch,
the trialcs->effective_xcpus field is now consistently computed and
maintained. Consequently, the legacy logic which assigned
**trialcs->allowed_cpus to a local 'xcpus' variable** when
trialcs->effective_xcpus was empty has been removed.

This removal is safe because when trialcs is not a partition member,
trialcs->effective_xcpus is now correctly populated with the intersection
of user_xcpus and the parent's effective_xcpus. This calculation inherently
covers the scenario previously handled by the removed code.

Signed-off-by: Chen Ridong <chenridong@...wei.com>
Reviewed-by: Waiman Long <longman@...hat.com>
---
 kernel/cgroup/cpuset.c | 64 +++++++++++++++++++++++++-----------------
 1 file changed, 38 insertions(+), 26 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index ab8572038fce..6107f657bf35 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2454,6 +2454,43 @@ static int cpus_allowed_validate_change(struct cpuset *cs, struct cpuset *trialc
 	return retval;
 }
 
+/**
+ * partition_cpus_change - Handle partition state changes due to CPU mask updates
+ * @cs: The target cpuset being modified
+ * @trialcs: The trial cpuset containing proposed configuration changes
+ * @tmp: Temporary masks for intermediate calculations
+ *
+ * This function handles partition state transitions triggered by CPU mask changes.
+ * CPU modifications may cause a partition to be disabled or require state updates.
+ */
+static void partition_cpus_change(struct cpuset *cs, struct cpuset *trialcs,
+					struct tmpmasks *tmp)
+{
+	enum prs_errcode prs_err;
+
+	if (cs_is_member(cs))
+		return;
+
+	prs_err = validate_partition(cs, trialcs);
+	if (prs_err)
+		trialcs->prs_err = cs->prs_err = prs_err;
+
+	if (is_remote_partition(cs)) {
+		if (trialcs->prs_err)
+			remote_partition_disable(cs, tmp);
+		else
+			remote_cpus_update(cs, trialcs->exclusive_cpus,
+					   trialcs->effective_xcpus, tmp);
+	} else {
+		if (trialcs->prs_err)
+			update_parent_effective_cpumask(cs, partcmd_invalidate,
+							NULL, tmp);
+		else
+			update_parent_effective_cpumask(cs, partcmd_update,
+							trialcs->effective_xcpus, tmp);
+	}
+}
+
 /**
  * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
  * @cs: the cpuset to consider
@@ -2467,7 +2504,6 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 	struct tmpmasks tmp;
 	bool force = false;
 	int old_prs = cs->partition_root_state;
-	enum prs_errcode prs_err;
 
 	retval = parse_cpuset_cpulist(buf, trialcs->cpus_allowed);
 	if (retval < 0)
@@ -2492,31 +2528,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 	 */
 	force = !cpumask_equal(cs->effective_xcpus, trialcs->effective_xcpus);
 
-	prs_err = validate_partition(cs, trialcs);
-	if (prs_err) {
-		trialcs->prs_err = prs_err;
-		cs->prs_err = prs_err;
-	}
-
-	if (is_partition_valid(cs) ||
-	   (is_partition_invalid(cs) && !trialcs->prs_err)) {
-		struct cpumask *xcpus = trialcs->effective_xcpus;
-
-		if (cpumask_empty(xcpus) && is_partition_invalid(cs))
-			xcpus = trialcs->cpus_allowed;
-
-		/*
-		 * Call remote_cpus_update() to handle valid remote partition
-		 */
-		if (is_remote_partition(cs))
-			remote_cpus_update(cs, NULL, xcpus, &tmp);
-		else if (trialcs->prs_err)
-			update_parent_effective_cpumask(cs, partcmd_invalidate,
-							NULL, &tmp);
-		else
-			update_parent_effective_cpumask(cs, partcmd_update,
-							xcpus, &tmp);
-	}
+	partition_cpus_change(cs, trialcs, &tmp);
 
 	spin_lock_irq(&callback_lock);
 	cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
-- 
2.34.1