cgroup/cpuset: Fix incorrect change to effective_xcpus in partition_xcpus_del()

[ Upstream commit f9a1767 ]

The effective_xcpus of a cpuset can contain offline CPUs. In
partition_xcpus_del(), the xcpus parameter is incorrectly used as
a temporary cpumask to mask out offline CPUs. As xcpus can be the
effective_xcpus of a cpuset, this can result in unexpected changes
in that cpumask. Fix this problem by not making any changes to the
xcpus parameter.

Fixes: 11e5f40 ("cgroup/cpuset: Keep track of CPUs in isolated partitions")
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Waiman-Long

kernel/cgroup/cpuset.c

@@ -1401,8 +1401,8 @@ static void partition_xcpus_del(int old_prs, struct cpuset *parent,
 		isolated_cpus_update(old_prs, parent->partition_root_state,
 				     xcpus);
 
-	cpumask_and(xcpus, xcpus, cpu_active_mask);
 	cpumask_or(parent->effective_cpus, parent->effective_cpus, xcpus);
+	cpumask_and(parent->effective_cpus, parent->effective_cpus, cpu_active_mask);
 }
 
 /*