linux-kernel - Re: [PATCH -next RFC 14/16] cpuset: fix isolcpus stay in root when isolated partition changes to root

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Message-ID: <7aeb1198-4c44-4395-9e09-971e0c8b6ef3@huaweicloud.com>
Date: Wed, 22 Oct 2025 18:49:53 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Waiman Long <llong@...hat.com>, tj@...nel.org, hannes@...xchg.org,
 mkoutny@...e.com
Cc: cgups@...r.kernel.org, linux-kernel@...r.kernel.org,
 lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [PATCH -next RFC 14/16] cpuset: fix isolcpus stay in root when
 isolated partition changes to root



On 2025/10/20 11:06, Waiman Long wrote:
> On 9/28/25 3:13 AM, Chen Ridong wrote:
>> From: Chen Ridong <chenridong@...wei.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 placed in an isolated partition. 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.
> 
> I am a bit confused at the beginning about this as it does not clearly state that CPU 9 was listed
> in the "isolcpus" boot command line parameter, but I believe this is what you mean here. Yes, there
> is a restriction that a boot time isolcpus CPU cannot be put into a non-isolated partition, though
> that will likely to be relaxed in the near future.
> 

Hi Longman,

Just to confirm, does this restriction also apply to remote partitions?

-- 
Best regards,
Ridong