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

[Glauber Costa]

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.