Re: [PATCH 00/10] cgroups: Task counter subsystem v8

From: Daniel Lezcano <daniel.lezcano@free.fr>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	"Aditya Kali" <adityakali@google.com>,
	"Daniel P. Berrange" <berrange@redhat.com>,
	"Max Kellermann" <mk@cm4all.com>,
	"Tim Hockin" <thockin@hockin.org>,
	"Glauber Costa" <glommer@gmail.com>,
	"Paul Menage" <paul@paulmenage.org>,
	"Daniel J Walsh" <dwalsh@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"Oleg Nesterov" <oleg@redhat.com>,
	"Mandeep Singh Baines" <msb@chromium.org>,
	Cgroups <cgroups@vger.kernel.org>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Tejun Heo" <tj@kernel.org>,
	Containers <containers@lists.linux-foundation.org>,
	"Papp Tamás" <tompos@martos.bme.hu>,
	"Ulli Horlacher" <framstag@rus.uni-stuttgart.de>
Subject: Re: [PATCH 00/10] cgroups: Task counter subsystem v8
Date: Thu, 01 Mar 2012 23:53:24 +0100	[thread overview]
Message-ID: <4F4FFDE4.8050908@free.fr> (raw)
In-Reply-To: <20120202145000.GC9071@somewhere.redhat.com>

On 02/02/2012 03:50 PM, Frederic Weisbecker wrote:
> On Wed, Feb 01, 2012 at 11:51:07AM -0800, Andrew Morton wrote:
>> On Wed, 1 Feb 2012 19:50:01 +0100
>> Frederic Weisbecker<fweisbec@gmail.com>  wrote:
>>
>>> On Wed, Feb 01, 2012 at 08:31:26AM -0800, Tejun Heo wrote:
>>>> On Wed, Feb 01, 2012 at 04:37:40AM +0100, Frederic Weisbecker wrote:
>>>>> Changes In this version:
>>>>>
>>>>> - Split 32/64 bits version of res_counter_write_u64() [1/10]
>>>>>    Courtesy of Kirill A. Shutemov
>>>>>
>>>>> - Added Kirill's ack [8/10]
>>>>>
>>>>> - Added selftests [9/10], [10/10]
>>>>>
>>>>> Please consider for merging. At least two users want this feature:
>>>> Has there been further discussion about this approach?  IIRC, we
>>>> weren't sure whether this should be merged.
>>> The doubts I have noticed were:
>>>
>>> Q: Can't we rather focus on a global solution to fight forkbombs?
>>>
>>> If we can find a reliable solution that works in any case and that
>>> prevent from any forkbomb to impact the rest of the system then it
>>> may be an acceptable solution. But I'm not aware of such feature.
>>>
>>> Besides, another point in having this task counter is that we
>>> have a per container limit. Assuming all containers are running under
>>> the same user, we can protect against a container starving all others
>>> with a massive amount of processes close to the NR_PROC rlimit.
>>>
>>> Q: Can/should we implement a limitation on the number of "fork" as well?
>>>     (as in https://lkml.org/lkml/2011/11/3/233 )
>>>
>>> I'm still not sure about why such a thing is needed. Is it really something we
>>> want? Why can't the task counter be used instead?
>>>
>>> I need more details from the author of this patch. But I doubt we can merge
>>> both subsystems, they have pretty different semantics.
>> What I struggle with is "is this feature useful enough to warrant
>> merging it"?
> The reason why I've been working on it is because we need this feature
> (at least) for LXC.

This feature is a recurrent request from the users of LXC. Recently, a 
container administrator complained an user was able to crash the entire 
host from a container.

http://sourceforge.net/mailarchive/message.php?msg_id=28915923

This feature is really useful to make the containers secure.

   -- Daniel

>
> Two people from our teams have jumped onto the discussion to express
> that they want this feature and why:
>
> https://lkml.org/lkml/2011/12/13/309
> https://lkml.org/lkml/2011/12/13/364
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