linux-kernel - [PATCH RFC v2 01/22] cpuset: fix isolcpus stay in root when isolated partition changes to root

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Message-Id: <20251025064844.495525-2-chenridong@huaweicloud.com>
Date: Sat, 25 Oct 2025 06:48:23 +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 RFC v2 01/22] cpuset: fix isolcpus stay in root when isolated partition changes to root

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

A bug was detected with the following steps:

  # cd /sys/fs/cgroup/
  # mkdir test
  # echo 9 > test/cpuset.cpus
  # echo isolated > test/cpuset.cpus.partition
  # cat test/cpuset.cpus.partition
  isolated
  # cat test/cpuset.cpus
  9
  # echo root > test/cpuset.cpus.partition
  # cat test/cpuset.cpus
  9
  # cat test/cpuset.cpus.partition
  root

CPU 9 was initially listed in the "isolcpus" boot command line parameter.
When the partition type is changed from isolated to root, CPU 9 remains
in what becomes a valid root partition. This violates the rule that
isolcpus can only be assigned to isolated partitions.

Fix this by adding a housekeeping conflict check during transitions
between root and isolated partitions.

Fixes: 4a74e418881f ("cgroup/cpuset: Check partition conflict with housekeeping setup")
Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 kernel/cgroup/cpuset.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 96104710a649..6af4d80b53c4 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2995,6 +2995,8 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 		 * Need to update isolated_cpus.
 		 */
 		isolcpus_updated = true;
+		if (prstate_housekeeping_conflict(new_prs, cs->effective_xcpus))
+			err = PERR_HKEEPING;
 	} else {
 		/*
 		 * Switching back to member is always allowed even if it
-- 
2.34.1