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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>
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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: <5B0F4F09.9050100@huawei.com>
Date:   Thu, 31 May 2018 09:25:29 +0800
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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.