linux-kernel - Re: [RFC PATCH-cgroup 5/6] cgroup: Skip dying css in cgroup_apply_control

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Date:   Wed, 21 Jun 2017 18:04:38 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com, pjt@...gle.com,
        luto@...capital.net, efault@....de, torvalds@...ux-foundation.org
Subject: Re: [RFC PATCH-cgroup 5/6] cgroup: Skip dying css in
 cgroup_apply_control_{enable,disable}

Hello,

On Wed, Jun 21, 2017 at 06:01:56PM -0400, Waiman Long wrote:
> I do think that it can happen with existing code because CSS killing is
> asynchronous, I think. So the command can complete before the CSS is
> actually gone. If the next command to reactivate it happens fast enough,
> we can trigger that. When I added more checking to my test script
> essentially increasing the latency between successive tests, I couldn't
> trigger it anymore.

While disabling is asynchronous, there's a flushing logic before
starting reenabling things, so the existing code shouldn't trigger
that condition.  But then there's should and the reality. :)

Thanks.

-- 
tejun