Re: [PATCH v3 1/3] cgroup/cpuset: return PERR_NOCPUS in remote_partition_enable()

[Ridong Chen <ridong.chen@linux.dev>]

On 9/21/2026 2:14 AM, Hui Peng wrote:
> Commit 6da580ec656a ("cgroup/cpuset: Don't allow creation of local
> partition over a remote one") updated update_prstate() to prevent creating
> a top-level local partition whose exclusive CPUs conflict with an existing
> remote partition.
> 
> However, if a top-level local partition A1 is created on CPUs 1-3, has a
> non-partition member child A1/A2 with cpuset.cpus.exclusive = 1-3, and a
> grandchild A1/A2/A3 is then enabled as a partition root on 1-3,
> update_prstate() sees !is_partition_valid(parent) (since A1/A2 is a member)
> and calls remote_partition_enable(). Because remote_partition_enable() does
> not check whether tmp->new_cpus intersects subpartitions_cpus, A1/A2/A3 is
> enabled as a remote partition on CPUs already owned by A1, triggering:
> 
>    WARNING: kernel/cgroup/cpuset.c:1594 at update_prstate+0xbef/0xd70
> 
> Return PERR_NOCPUS in remote_partition_enable() when tmp->new_cpus
> intersects subpartitions_cpus, matching the error code used by
> remote_cpus_update() for subpartitions_cpus conflicts, and add a
> corresponding regression test case to
> tools/testing/selftests/cgroup/test_cpuset_prs.sh.
> 
> Tested in QEMU on Linux 7.3.0-rc3 using
> tools/testing/selftests/cgroup/test_cpuset_prs.sh.
> 
> Fixes: 6da580ec656a ("cgroup/cpuset: Don't allow creation of local partition over a remote one")
> Suggested-by: Guopeng Zhang <guopeng.zhang@linux.dev>
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Hui Peng <benquike@gmail.com>
> ---
> Changes in v3:
> - Split the series into 3 patches (one per logical change and Fixes: tag).
> 

What is going on here?

Please do not reply with a new series. And I think the changes should be listed 
in the cover letter. Otherwise, it will get very confusing.


>   kernel/cgroup/cpuset.c                        | 4 +++-
>   tools/testing/selftests/cgroup/test_cpuset_prs.sh | 2 ++
>   2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index c8ab89cfbe3d..7381fa8502e7 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1678,8 +1678,10 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
>   	 * Callers must have validated that effective_xcpus is not empty.
>   	 */
>   	spin_lock_irq(&callback_lock);
> -	if (cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus)) {
> +	if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus) ||
> +	    cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus)) {
>   		spin_unlock_irq(&callback_lock);
> +		if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus))
> +			return PERR_NOCPUS;
>   		return PERR_HKEEPING;
>   	}
>   

I cannot apply this patch. It seems quite different from v2.

> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index a1f42ef64bc1..b732078bf319 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -298,6 +298,8 @@ TEST_MATRIX=(
>   	" C0-4:X2-4 C1-4:X2-4:P2 C2-4:X4:P1 \
>   				   .      .      .      X1      .    0 A1:0-1|A2:2-4|A3:2-4 \
>   								       A1:P0|A2:P2|A3:P-1 2-4"
> +	" CX1-3:P1 CX1-3  CX1-3    .      .      .      P1     .     0 A1:1-3|A2:1-3|A3:1-3 \
> +								       A1:P1|A2:P0|A3:P-1"
>   
>   	# Remote partition offline tests
>   	"   C0-3    C1-3  C2-3     .    X2-3   X2-3 X2-3:P2:O2=0 .   0 A1:0-1|A2:1|A3:3 A1:P0|A3:P2 2-3"

-- 
Best regards
Ridong