Re: [PATCH v4 2/3] cgroup/cpuset: prevent activating local partition over remote one

[Waiman Long <longman@redhat.com>]

On 9/27/26 9:40 PM, Ridong Chen wrote:
>
>
> On 9/24/2026 12:27 PM, Hui Peng wrote:
>> Commit 6da580ec656a ("cgroup/cpuset: Don't allow creation of local
>> partition over a remote one") added a check in update_prstate() to 
>> reject
>> creating a top-level local partition whose cs->exclusive_cpus intersects
>> subpartitions_cpus.
>>
>> However, if a top-level cgroup A1 has a child A1/A2 enabled as a remote
>> partition on a subset of its exclusive CPUs (X2-3 on A1, CX2-3:P2 on
>> A1/A2), and A1 is then set to "root" (P1, becoming "root invalid" via
>> update_prstate() because its exclusive CPUs intersect 
>> subpartitions_cpus)
>> followed by expanding its CPUs to include additional non-remote CPUs
>> (CX1-3), update_cpumask() / update_exclusive_cpumask() calls
>> validate_partition() without going through update_prstate(). Because
>> validate_partition() does not check trialcs->exclusive_cpus against
>> subpartitions_cpus, A1 transitions from "root invalid" to a valid local
>> partition over the existing remote partition A1/A2 and triggers:
>>
>>    WARNING: kernel/cgroup/cpuset.c:1943 at 
>> update_parent_effective_cpumask+0x189b/0x1fd0
>>
>> Check trialcs->exclusive_cpus against subpartitions_cpus in
>> validate_partition() when !is_partition_valid(cs), and add a regression
>> test case to tools/testing/selftests/cgroup/test_cpuset_prs.sh.
>>
>
> Was this message assisted by an LLM?
>
> It would be helpful if you could provide the reproducer as I replied 
> earlier, so that it can be understood more easily and tested.

The provided test case for test-cpuset_prs.sh is supposed to be the 
reproducer if you don't have deadline task running in the test system or 
the kernel includes the last cpuset patch that I sent out.

Cheers,
Longman