linux-kernel - Re: [PATCH 11/11] protect architectures where THREAD_SIZE >= PAGE

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Message-ID: <4FE9BB25.60905@parallels.com>
Date:	Tue, 26 Jun 2012 17:37:41 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Tejun Heo <tj@...nel.org>,
	Frederic Weisbecker <fweisbec@...hat.com>,
	<cgroups@...r.kernel.org>, <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>, <devel@...nvz.org>,
	<kamezawa.hiroyu@...fujitsu.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH 11/11] protect architectures where THREAD_SIZE >= PAGE_SIZE
 against fork bombs

On 06/26/2012 05:38 PM, Frederic Weisbecker wrote:
> On Tue, Jun 26, 2012 at 04:48:08PM +0400, Glauber Costa wrote:
>> On 06/25/2012 10:38 PM, Tejun Heo wrote:
>>> On Mon, Jun 25, 2012 at 06:55:35PM +0200, Frederic Weisbecker wrote:
>>>> On 06/25/2012 04:15 PM, Glauber Costa wrote:
>>>>
>>>>> Because those architectures will draw their stacks directly from
>>>>> the page allocator, rather than the slab cache, we can directly
>>>>> pass __GFP_KMEMCG flag, and issue the corresponding free_pages.
>>>>>
>>>>> This code path is taken when the architecture doesn't define
>>>>> CONFIG_ARCH_THREAD_INFO_ALLOCATOR (only ia64 seems to), and has
>>>>> THREAD_SIZE >= PAGE_SIZE. Luckily, most - if not all - of the
>>>>> remaining architectures fall in this category.
>>>>>
>>>>> This will guarantee that every stack page is accounted to the memcg
>>>>> the process currently lives on, and will have the allocations to fail
>>>>> if they go over limit.
>>>>>
>>>>> For the time being, I am defining a new variant of THREADINFO_GFP, not
>>>>> to mess with the other path. Once the slab is also tracked by memcg,
>>>>> we can get rid of that flag.
>>>>>
>>>>> Tested to successfully protect against :(){ :|:& };:
>>>>>
>>>>> Signed-off-by: Glauber Costa <glommer@...allels.com>
>>>>> CC: Christoph Lameter <cl@...ux.com>
>>>>> CC: Pekka Enberg <penberg@...helsinki.fi>
>>>>> CC: Michal Hocko <mhocko@...e.cz>
>>>>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>>>>> CC: Johannes Weiner <hannes@...xchg.org>
>>>>> CC: Suleiman Souhlal <suleiman@...gle.com>
>>>>
>>>>
>>>> Acked-by: Frederic Weisbecker <fweisbec@...hat.com>
>>>
>>> Frederic, does this (with proper slab accounting added later) achieve
>>> what you wanted with the task counter?
>>>
>>
>> A note: Frederic may confirm, but I think he doesn't even need
>> the slab accounting to follow to achieve that goal.
>
> Limiting is enough. But that requires internal accounting.
>
Yes, but why the *slab* needs to get involved?
accounting task stack pages should be equivalent to what you
were doing, even without slab accounting. Right ?


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