Commit 345f40166694 for kernel

commit 345f40166694e60db6d5cf02233814bb27ac5dec
Author: sunshaojie <sunshaojie@kylinos.cn>
Date:   Wed May 13 18:37:38 2026 +0800

    cgroup/cpuset: Return only actually allocated CPUs during partition invalidation

    In update_parent_effective_cpumask() with partcmd_invalidate, the CPUs
    to return to the parent are computed as:

        adding = cpumask_and(tmp->addmask, xcpus, parent->effective_xcpus);

    where xcpus = user_xcpus(cs) which returns cs->exclusive_cpus (if set)
    or cs->cpus_allowed. When exclusive_cpus is not set, user_xcpus(cs) can
    contain CPUs that were never actually granted to the partition due to
    sibling exclusion in compute_excpus(). Consequently, the invalidation
    may return CPUs to the parent that remain in use by sibling partitions,
    causing overlapping effective_cpus and triggering the
    WARN_ON_ONCE(1) in generate_sched_domains().

    Use cs->effective_xcpus instead, which reflects the CPUs actually
    granted to this partition.

    Reproducer (on a 4-CPU machine):

        cd /sys/fs/cgroup
        mkdir a1 b1

        # a1 becomes partition root with CPUs 0-1
        echo "0-1" > a1/cpuset.cpus
        echo "root" > a1/cpuset.cpus.partition

        # b1 becomes partition root with CPUs 1-2, but sibling exclusion
        # reduces its effective_xcpus to CPU 2 only
        echo "1-2" > b1/cpuset.cpus
        echo "root" > b1/cpuset.cpus.partition

        # b1 changes cpus_allowed to 0-1 -> partition invalidation
        echo "0-1" > b1/cpuset.cpus

        # Expected: CPUs 2-3  (only CPU 2 returned from b1)
        # Actual:   CPUs 1-3  (CPU 0-1 returned, overlapping with a1)
        cat cpuset.cpus.effective

    dmesg will also show a WARNING from generate_sched_domains() reporting
    overlapping partition root effective_cpus.

    Fixes: 2a3602030d80 ("cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict")
    Cc: stable@vger.kernel.org # v7.0+
    Signed-off-by: sunshaojie <sunshaojie@kylinos.cn>
    Tested-by: Chen Ridong <chenridong@huaweicloud.com>
    Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
    Reviewed-by: Waiman Long <longman@redhat.com>
    Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index e84e801e22cf..5c33ab20cc20 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1718,7 +1718,8 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 		 */
 		if (is_partition_valid(parent))
 			adding = cpumask_and(tmp->addmask,
-					     xcpus, parent->effective_xcpus);
+					     cs->effective_xcpus,
+					     parent->effective_xcpus);
 		if (old_prs > 0)
 			new_prs = -old_prs;