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

[Waiman Long <llong@redhat.com>]

On 10/25/25 2:48 AM, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.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@huawei.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

This patch has been merged in somewhat different form.

Cheers,
Longman