cpuset: fix failure to enable isolated partition when containing isolcpus

[ Upstream commit 216217e ]

The 'isolcpus' parameter specified at boot time can be assigned to an
isolated partition. While it is valid put the 'isolcpus' in an isolated
partition, attempting to change a member cpuset to an isolated partition
will fail if the cpuset contains any 'isolcpus'.

For example, the system boots with 'isolcpus=9', and the following
configuration works correctly:

  # cd /sys/fs/cgroup/
  # mkdir test
  # echo 1 > test/cpuset.cpus
  # echo isolated > test/cpuset.cpus.partition
  # cat test/cpuset.cpus.partition
  isolated
  # echo 9 > test/cpuset.cpus
  # cat test/cpuset.cpus.partition
  isolated
  # cat test/cpuset.cpus
  9

However, the following steps to convert a member cpuset to an isolated
partition will fail:

  # cd /sys/fs/cgroup/
  # mkdir test
  # echo 9 > test/cpuset.cpus
  # echo isolated > test/cpuset.cpus.partition
  # cat test/cpuset.cpus.partition
  isolated invalid (partition config conflicts with housekeeping setup)

The issue occurs because the new partition state (new_prs) is used for
validation against housekeeping constraints before it has been properly
updated. To resolve this, move the assignment of new_prs before the
housekeeping validation check when enabling a root partition.

Fixes: 4a74e41 ("cgroup/cpuset: Check partition conflict with housekeeping setup")
Signed-off-by: Chen Ridong <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: Chen Ridong

kernel/cgroup/cpuset.c

@@ -1716,6 +1716,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 		xcpus = tmp->delmask;
 		if (compute_effective_exclusive_cpumask(cs, xcpus, NULL))
 			WARN_ON_ONCE(!cpumask_empty(cs->exclusive_cpus));
+		new_prs = (cmd == partcmd_enable) ? PRS_ROOT : PRS_ISOLATED;
 
 		/*
 		 * Enabling partition root is not allowed if its
@@ -1748,7 +1749,6 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 
 		deleting = true;
 		subparts_delta++;
-		new_prs = (cmd == partcmd_enable) ? PRS_ROOT : PRS_ISOLATED;
 	} else if (cmd == partcmd_disable) {
 		/*
 		 * May need to add cpus back to parent's effective_cpus