Re: [PATCH-next v3 1/9] cgroup/cpuset: Fix a missing isolated_cpus update in update_cpumasks_hier()

[Waiman Long <longman@redhat.com>]

On 10/15/26 9:02 AM, Guopeng Zhang wrote:
>
> 在 2026/10/14 22:05, Waiman Long 写道:
>> It is found that when a local isolated partition is being invalidated
>> because its root partition parent is no longer valid, the isolated_cpus
>> cpumask may not be properly updated. If the parent was previously
>> an isolated partition, its invalidation should have properly updated
>> isolated_cpus before and no action will be needed.
>>
>> Fix that by calling isolated_cpus_update() in this invalidation case
>> to update isolated_cpus. A test case in test_cpuset_prs.sh is modified
>> to test that.
>>
>> Fixes: 11e5f407b64a ("cgroup/cpuset: Keep track of CPUs in isolated partitions")
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> ---
>>   kernel/cgroup/cpuset.c                        | 19 ++++++++++++++-----
>>   .../selftests/cgroup/test_cpuset_prs.sh       |  4 ++--
>>   2 files changed, 16 insertions(+), 7 deletions(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 0ebba2d646c3..6b5c870e5607 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -2229,7 +2229,9 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
>>   		 * cpuset if the parent's effective_cpus changes.
>>   		 */
>>   		if ((cp != cs) && old_prs) {
>> -			switch (parent->partition_root_state) {
>> +			int parent_prs = parent->partition_root_state;
>> +
>> +			switch (parent_prs) {
>>   			case PRS_ROOT:
>>   			case PRS_ISOLATED:
>>   				update_parent = true;
>> @@ -2238,11 +2240,18 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
>>   			default:
>>   				/*
>>   				 * When parent is not a partition root or is
>> -				 * invalid, child partition roots become
>> -				 * invalid too.
>> +				 * invalid, child partition roots become invalid
>> +				 * too. For an isolated partition with root
>> +				 * partition parent, isolated_cpus_updated()
>> +				 * is called to update isolated_cpus.
>>   				 */
>> -				if (is_partition_valid(cp))
>> -					new_prs = -cp->partition_root_state;
>> +				if (is_partition_valid(cp)) {
>> +					new_prs = -old_prs;
>> +					if ((old_prs == PRS_ISOLATED) &&
>> +					    (parent_prs == -PRS_ROOT))
>> +						isolated_cpus_update(old_prs, new_prs,
>> +								     cp->effective_xcpus);
>> +				}
> I tested switching a parent partition from root to member and found that
> CPUs can remain listed in cpuset.cpus.isolated. CPUs 0-15 are online, with
> nohz_full=2-15 and no isolcpus:
>
>      # cd /sys/fs/cgroup
>      # echo +cpuset > cgroup.subtree_control
>      # mkdir A
>      # echo 1-2 > A/cpuset.cpus
>      # echo root > A/cpuset.cpus.partition
>      # echo +cpuset > A/cgroup.subtree_control
>      # mkdir A/C
>      # echo 2 > A/C/cpuset.cpus
>      # echo isolated > A/C/cpuset.cpus.partition
>      # cat cpuset.cpus.isolated
>      2
>      # echo member > A/cpuset.cpus.partition
>      # cat A/C/cpuset.cpus.partition
>      isolated invalid (Parent is not a partition root)
>      # cat cpuset.cpus.isolated
>      2
>
> A is now a member and C is invalid, so cpuset.cpus.isolated should be
> empty here, but CPU 2 remains.

Yes, this patch isn't quite correct and can't catch some corner cases. I 
have a new version that should work much better and I can't reproduce 
your test case with the new patch. I will send out a v4 soon.

Cheers,
Longman

> Thanks,
> Guopeng>  				WRITE_ONCE(cp->prs_err,
>>   					   is_partition_invalid(parent)
>>   					   ? PERR_INVPARENT : PERR_NOTPART);
>> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
>> index 7efd5e645767..874a8a161236 100755
>> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
>> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
>> @@ -292,9 +292,9 @@ TEST_MATRIX=(
>>   								       A1:P0|A2:P2|A3:P1 2-4|2-3"
>>   	"   C0-4    C1-4  C2-4     .    X2-4  X2-4:P2 X3-4:P1   .    0 A1:0-1|A2:2|A3:3-4 \
>>   								       A1:P0|A2:P2|A3:P1 2"
>> -	" C0-4:X2-4 C1-4:X2-4:P2 C2-4:X4:P1 \
>> +	" C0-4:X2-4 C1-4:X2-4:P1 C2-4:X4:P2 \
>>   				   .      .      X5      .      .    0 A1:0-4|A2:1-4|A3:2-4 \
>> -								       A1:P0|A2:P-2|A3:P-1 ."
>> +								       A1:P0|A2:P-1|A3:P-2 ."
>>   	" 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"