linux-kernel - [PATCH -next 01/11] cpuset: move the root cpuset write check earlier

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Message-Id: <20250917060454.2885698-2-chenridong@huaweicloud.com>
Date: Wed, 17 Sep 2025 06:04:44 +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 01/11] cpuset: move the root cpuset write check earlier

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

The 'cpus' or 'mems' lists of the top_cpuset cannot be modified.
This check can be moved before acquiring any locks as a common code
block to improve efficiency and maintainability.

Signed-off-by: Chen Ridong <chenridong@...wei.com>
Reviewed-by: Waiman Long <longman@...hat.com>
---
 kernel/cgroup/cpuset.c | 17 ++++-------------
 1 file changed, 4 insertions(+), 13 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 0d41b4993f8c..819adf4fd591 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2338,10 +2338,6 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 	bool force = false;
 	int old_prs = cs->partition_root_state;
 
-	/* top_cpuset.cpus_allowed tracks cpu_active_mask; it's read-only */
-	if (cs == &top_cpuset)
-		return -EACCES;
-
 	/*
 	 * An empty cpus_allowed is ok only if the cpuset has no tasks.
 	 * Since cpulist_parse() fails on an empty mask, we special case
@@ -2802,15 +2798,6 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
 {
 	int retval;
 
-	/*
-	 * top_cpuset.mems_allowed tracks node_stats[N_MEMORY];
-	 * it's read-only
-	 */
-	if (cs == &top_cpuset) {
-		retval = -EACCES;
-		goto done;
-	}
-
 	/*
 	 * An empty mems_allowed is ok iff there are no tasks in the cpuset.
 	 * Since nodelist_parse() fails on an empty mask, we special case
@@ -3280,6 +3267,10 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
 	struct cpuset *trialcs;
 	int retval = -ENODEV;
 
+	/* root is read-only */
+	if (cs == &top_cpuset)
+		return -EACCES;
+
 	buf = strstrip(buf);
 	cpuset_full_lock();
 	if (!is_cpuset_online(cs))
-- 
2.34.1