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

[Frederic Weisbecker]

On Tue, Jun 26, 2012 at 05:37:41PM +0400, Glauber Costa wrote:
> 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 ?

Yeah that alone should be fine.