From: Chen Ridong <chenridong@huawei.com>

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

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 44231cb1d83f..2b7e2f17577e 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1806,6 +1806,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 		xcpus = tmp->delmask;
 		if (compute_excpus(cs, xcpus))
 			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
@@ -1838,7 +1839,6 @@ 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
-- 
2.34.1

On 9/18/25 9:12 PM, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.com>
>
> 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: 4a74e418881f ("cgroup/cpuset: Check partition conflict with housekeeping setup")
> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> ---
>   kernel/cgroup/cpuset.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 44231cb1d83f..2b7e2f17577e 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1806,6 +1806,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
>   		xcpus = tmp->delmask;
>   		if (compute_excpus(cs, xcpus))
>   			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
> @@ -1838,7 +1839,6 @@ 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
Reviewed-by: Waiman Long <longman@redhat.com>