linux-kernel - Re: [PATCHv9 1/3] rdmacg: Added rdma cgroup controller

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Date:	Thu, 3 Mar 2016 14:01:43 +0530
From:	Parav Pandit <pandit.parav@...il.com>
To:	Haggai Eran <haggaie@...lanox.com>
Cc:	Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-rdma@...r.kernel.org, lizefan@...wei.com,
	Johannes Weiner <hannes@...xchg.org>,
	Doug Ledford <dledford@...hat.com>,
	Liran Liss <liranl@...lanox.com>,
	"Hefty, Sean" <sean.hefty@...el.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Jonathan Corbet <corbet@....net>, james.l.morris@...cle.com,
	serge@...lyn.com, Or Gerlitz <ogerlitz@...lanox.com>,
	Matan Barak <matanb@...lanox.com>, raindel@...lanox.com,
	akpm@...ux-foundation.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCHv9 1/3] rdmacg: Added rdma cgroup controller

On Thu, Mar 3, 2016 at 1:44 PM, Haggai Eran <haggaie@...lanox.com> wrote:
> On 03/03/2016 05:18, Parav Pandit wrote:
>> On Thu, Mar 3, 2016 at 1:28 AM, Parav Pandit <pandit.parav@...il.com> wrote:
>>> On Wed, Mar 2, 2016 at 11:09 PM, Tejun Heo <tj@...nel.org> wrote:
>>>> Nothing seems to prevent @cg from going away if this races with
>>>> @current being migrated to a different cgroup.  Have you run this with
>>>> lockdep and rcu debugging enabled?  This should have triggered a
>>>> warning.
>> I am able to reproduce this race. Looking into how to address it.
>
> If I understand correctly, task_css() requires rcu read lock being held.
> Is task_get_css() suitable here?

Yes. Its suitable if we continue with newer API to drop "num" entries.
Or I will have make minor modification to support that in cgroup.h.
There is no variation as task_get_css_many, but its minor change anyway.
I saw slept off yesterday night, saw today morning.
Will test over weekend and wait for Tejun's opinion if there is any.