Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] cpuset: Enforce that a child's cpus must be a subset of
 the parent
To:     Waiman Long <longman@redhat.com>, Tejun Heo <tj@kernel.org>,
        "Johannes Weiner" <hannes@cmpxchg.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Ingo Molnar" <mingo@redhat.com>
References: <1527687991-1431-1-git-send-email-longman@redhat.com>
 <5B0F4F09.9050100@huawei.com>
CC:     <cgroups@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-doc@vger.kernel.org>, <kernel-team@fb.com>,
        <pjt@google.com>, <luto@amacapital.net>,
        Mike Galbraith <efault@gmx.de>,
        <torvalds@linux-foundation.org>, Roman Gushchin <guro@fb.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Patrick Bellasi <patrick.bellasi@arm.com>
From:   Zefan Li <lizefan@huawei.com>
Message-ID: <5B0FAE72.1090204@huawei.com>
Date:   Thu, 31 May 2018 16:12:34 +0800
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101
 Thunderbird/38.5.1
MIME-Version: 1.0
In-Reply-To: <5B0F4F09.9050100@huawei.com>
Content-Type: text/plain; charset="gbk"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2018/5/31 9:25, Zefan Li wrote:
> Hi Waiman,
> 
> On 2018/5/30 21:46, Waiman Long wrote:
>> It was found that the cpuset.cpus could contain CPUs that are not listed
>> in their parent's cpu list as shown by the command sequence below:
>>
>>   # echo "+cpuset" >cgroup.subtree_control
>>   # mkdir g1
>>   # echo 0-5 >g1/cpuset.cpus
>>   # mkdir g1/g11
>>   # echo "+cpuset" > g1/cgroup.subtree_control
>>   # echo 6-11 >g1/g11/cpuset.cpus
>>   # grep -R . g1 | grep "\.cpus"
>>   g1/cpuset.cpus:0-5
>>   g1/cpuset.cpus.effective:0-5
>>   g1/g11/cpuset.cpus:6-11
>>   g1/g11/cpuset.cpus.effective:0-5
>>
>> As the intersection of g11's cpus and that of g1 is empty, the effective
>> cpus of g11 is just that of g1. The check in update_cpumask() is now
>> corrected to make sure that cpus in a child cpus must be a subset of
>> its parent's cpus. The error "write error: Invalid argument" will now
>> be reported in the above case.
>>
> 
> We made the distinction between user-configured CPUs and effective CPUs
> in commit 7e88291beefbb758, so actually it's not a bug.
> 

I remember the original reason is to support restoration of the original
cpu after cpu offline->online. We use user-configured CPUs to remember
if the cpu should be restored in the cpuset after it's onlined.