[Devel] Re: [PATCH 11/11] protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs

[Glauber Costa]

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 at parallels.com>
>>>>> CC: Christoph Lameter <cl at linux.com>
>>>>> CC: Pekka Enberg <penberg at cs.helsinki.fi>
>>>>> CC: Michal Hocko <mhocko at suse.cz>
>>>>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
>>>>> CC: Johannes Weiner <hannes at cmpxchg.org>
>>>>> CC: Suleiman Souhlal <suleiman at google.com>
>>>>
>>>>
>>>> Acked-by: Frederic Weisbecker <fweisbec at redhat.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 ?