linux-kernel - Re: [PATCH v2] cpuset: restore sanity to cpuset_cpus_allowed

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Date:   Tue, 21 May 2019 16:34:14 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Joel Savitz <jsavitz@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
        Tejun Heo <tj@...nel.org>, Waiman Long <longman@...hat.com>,
        Phil Auld <pauld@...hat.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH v2] cpuset: restore sanity to
 cpuset_cpus_allowed_fallback()

On Tue, Apr 09, 2019 at 04:40:03PM -0400, Joel Savitz <jsavitz@...hat.com> wrote:
> 	$ grep Cpus /proc/$$/status
> 	Cpus_allowed:	ff
> 	Cpus_allowed_list:	0-7

(a)
 
> 	$ taskset -p 4 $$
> 	pid 19202's current affinity mask: f
> 	pid 19202's new affinity mask: 4
> 
> 	$ grep Cpus /proc/self/status
> 	Cpus_allowed:	04
> 	Cpus_allowed_list:	2
> 
> 	# echo off > /sys/devices/system/cpu/cpu2/online
> 	$ grep Cpus /proc/$$/status
> 	Cpus_allowed:	0b
> 	Cpus_allowed_list:	0-1,3
I'm confused where this value comes from, I must be missing something.

Joel, is the task in question put into a cpuset with 0xf CPUs only (at
point (a))? Or are the CPUs 4-7 offlined as well?

Thanks,
Michal