linux-kernel - cpusets in non-unified hierarchy broken?

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Date:	Thu, 12 Feb 2015 21:49:51 +0000
From:	Serge Hallyn <serge.hallyn@...ntu.com>
To:	linux-kernel@...r.kernel.org, tj@...nel.org, lizefan@...wei.com
Cc:	Stéphane Graber <stgraber@...ntu.com>,
	christianvanbrauner@...il.com
Subject: cpusets in non-unified hierarchy broken?

Hi,

as of some point in 3.18, cpuset.cpus doesn't seem to be
enforced any more.  I don't see an obvious reason in the
code, but it seems likely to be related to the effective_cpus.

If I mount -t cgroup -o cpuset cpuset /mnt and then mkdir /mnt/lxc,
then /mnt/lxc has:

====================================================
ubuntu@...set1:~$ cat /mnt/lxc/cpuset.effective_cpus

ubuntu@...set1:~$ cat /mnt/lxc/cpuset.cpus
0-3
====================================================

while

====================================================
ubuntu@...set1:~$ cat /mnt/cpuset.effective_cpus
0-3
ubuntu@...set1:~$ cat /mnt/cpuset.cpus
0-3
====================================================

My understanding is that effective_cpus in /lxc should be
the /cpuset.effective_cpus & /lxc/cpuset.cpus.  But that
doesn't seem to be the case.  So then, when I start a
container confined to a single cpu (which will use cgroup
/lxc/c1, for instance) then it looks like:

====================================================
ubuntu@...set1:~$ cat /mnt/lxc/v1/cpuset.effective_cpus

ubuntu@...set1:~$ cat /mnt/lxc/v1/cpuset.cpus
1
====================================================

While the /proc/self/status inside that container and cgroup
shows:

====================================================
root@v1:~# grep -i cpu /proc/self/status
Cpus_allowed:   f
Cpus_allowed_list:      0-3
====================================================

Christian, who originally found this and reported it at
https://github.com/lxc/lxc/issues/427 , also tested that in fact
the tasks are not confined (so it's not just an issue of
improper reporting, it seems)

thanks,
-serge
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