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[95.157.63.22]) by smtp.gmail.com with ESMTPSA id k25-v6sm25540439wre.18.2018.10.16.08.11.42 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Oct 2018 08:11:42 -0700 (PDT) Cc: mtk.manpages@gmail.com, "open list:CONTROL GROUP (CGROUP)" , "Serge E. Hallyn" , lkml Subject: Re: Cgroup v2 thread mode oddity: "domain invalid" cgroup with threaded controller enabled To: Tejun Heo References: From: "Michael Kerrisk (man-pages)" Message-ID: <4fd48929-69fa-f13b-0095-1d210068684d@gmail.com> Date: Tue, 16 Oct 2018 17:11:41 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Tejun, A ping on the below... Thanks, Michael On 10/04/2018 09:40 PM, Michael Kerrisk (man-pages) wrote: > Hello Tejun, > > Suppose we have the following scenario: > > x [d] (pids) > y [dt] (pids) > p [t] > q [t] > r [t] > z [d] > > Here, x/y is a "domain threaded root" with a threaded controller > (the 'pids' controller) enabled. (In this scenario, there are no > member processes in any of the cgroups.) > > Suppose we now convert x/z to "threaded" type: > > # echo threaded > x/z/cgroup.type > > Now we end up in the following state: > > x [dt] (pids) > y [inv] (pids) > p [t] > q [t] > r [t] > z [t] > > This seems odd. x/y is now of "domain invalid" type with a controller > enabled! This feels like a violation of the rules, since we can't > in other circumstances do anything with a "domain invalid" cgroup > except convert it to "threaded". In particular, we can't create > child cgroups under a "domain invalid" cgroup, or add member processes > to the cgroup, or *enable controllers in the cgroup*. In fact, when > doing the > > # echo threaded > x/z/cgroup.type > > I had expected a write(2) error because the state of x/y should > (I thought) not be permitted. > > Your thoughts? > > Thanks, > > Michael > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/