linux-kernel - Re: [PATCH -next] cpuset: treate root invalid trialcs as exclusive

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Message-ID: <a16c91d9-a779-44e5-9ca6-e14e7540ed69@huaweicloud.com>
Date: Mon, 17 Nov 2025 14:23:43 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Sun Shaojie <sunshaojie@...inos.cn>
Cc: cgroups@...r.kernel.org, hannes@...xchg.org,
 linux-kernel@...r.kernel.org, longman@...hat.com, mkoutny@...e.com,
 tj@...nel.org
Subject: Re: [PATCH -next] cpuset: treate root invalid trialcs as exclusive



On 2025/11/17 12:35, Sun Shaojie wrote:
> On 2025/11/15 09:31, Chen Ridong wrote:
>> A test scenario revealed inconsistent results based on operation order:
>> Scenario 1:
>> 	#cd /sys/fs/cgroup/
>> 	#mkdir A1
>> 	#mkdir B1
>> 	#echo 1-2 > B1/cpuset.cpus
>> 	#echo 0-1 > A1/cpuset.cpus
>> 	#echo root > A1/cpuset.cpus.partition
>> 	#cat A1/cpuset.cpus.partition
>> 	root invalid (Cpu list in cpuset.cpus not exclusive)
>>
>> Scenario 2:
>> 	#cd /sys/fs/cgroup/
>> 	#mkdir A1
>> 	#mkdir B1
>> 	#echo 1-2 > B1/cpuset.cpus
>> 	#echo root > A1/cpuset.cpus.partition
>> 	#echo 0-1 > A1/cpuset.cpus
>> 	#cat A1/cpuset.cpus.partition
>> 	root
>>
>> The second scenario produces an unexpected result: A1 should be marked
>> as invalid but is incorrectly recognized as valid. This occurs because
>> when validate_change is invoked, A1 (in root-invalid state) may
>> automatically transition to a valid partition, with non-exclusive state
>> checks against siblings, leading to incorrect validation.
>>
>> To fix this inconsistency, treat trialcs in root-invalid state as exclusive
>> during validation and set the corresponding exclusive flags, ensuring
>> consistent behavior regardless of operation order.
>>
>> Signed-off-by: Chen Ridong <chenridong@...wei.com>
>> ---
>> kernel/cgroup/cpuset.c | 19 ++++++++++++++-----
>> 1 file changed, 14 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index daf813386260..a189f356b5f1 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -2526,6 +2526,18 @@ static void partition_cpus_change(struct cpuset *cs, struct cpuset *trialcs,
>> 	}
>> }
>>
>> +static int init_trialcs(struct cpuset *cs, struct cpuset *trialcs)
>> +{
>> +	trialcs->prs_err = PERR_NONE;
>> +	/*
>> +	 * If partition_root_state != 0, it may automatically change to a partition,
>> +	 * Therefore, we should treat trialcs as exclusive during validation
>> +	 */
>> +	if (trialcs->partition_root_state)
>> +		set_bit(CS_CPU_EXCLUSIVE, &trialcs->flags);
>> +	return compute_trialcs_excpus(trialcs, cs);
>> +}
>> +
>> /**
>>  * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
>>  * @cs: the cpuset to consider
>> @@ -2551,9 +2563,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>> 	if (alloc_tmpmasks(&tmp))
>> 		return -ENOMEM;
>>
>> -	compute_trialcs_excpus(trialcs, cs);
>> -	trialcs->prs_err = PERR_NONE;
>> -
>> +	init_trialcs(cs, trialcs);
>> 	retval = cpus_allowed_validate_change(cs, trialcs, &tmp);
>> 	if (retval < 0)
>> 		goto out_free;
>> @@ -2612,7 +2622,7 @@ static int update_exclusive_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>> 	 * Reject the change if there is exclusive CPUs conflict with
>> 	 * the siblings.
>> 	 */
>> -	if (compute_trialcs_excpus(trialcs, cs))
>> +	if (init_trialcs(cs, trialcs))
>> 		return -EINVAL;
>>
>> 	/*
>> @@ -2628,7 +2638,6 @@ static int update_exclusive_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>> 	if (alloc_tmpmasks(&tmp))
>> 		return -ENOMEM;
>>
>> -	trialcs->prs_err = PERR_NONE;
>> 	partition_cpus_change(cs, trialcs, &tmp);
>>
>> 	spin_lock_irq(&callback_lock);
> 
> Hi, Ridong,
> 
> Maybe, this patch does not apply to the following cases:
>  Step
>  #1> echo "root" > A1/cpuset.cpus.partition
>  #1> echo "0-1" > B1/cpuset.cpus
>  #2> echo "1-2" > A1/cpuset.cpus.exclusive  -> return error
>  It should return success here.
> 
> Please consider the following modification.
> 

If A1 will automatically change to a valid partition, I think it should return error.

Thanks.

-- 
Best regards,
Ridong