[Devel] Re: [PATCH v2 11/11] protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs

[Kamezawa Hiroyuki]

(2012/08/09 22:01), 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>
> Acked-by: Frederic Weisbecker <fweisbec at redhat.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: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>


> ---
>   include/linux/thread_info.h | 2 ++
>   kernel/fork.c               | 4 ++--
>   2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> index ccc1899..e7e0473 100644
> --- a/include/linux/thread_info.h
> +++ b/include/linux/thread_info.h
> @@ -61,6 +61,8 @@ extern long do_no_restart_syscall(struct restart_block *parm);
>   # define THREADINFO_GFP		(GFP_KERNEL | __GFP_NOTRACK)
>   #endif
>   
> +#define THREADINFO_GFP_ACCOUNTED (THREADINFO_GFP | __GFP_KMEMCG)
> +
>   /*
>    * flag set/clear/test wrappers
>    * - pass TIF_xxxx constants to these functions
> diff --git a/kernel/fork.c b/kernel/fork.c
> index dc3ff16..b0b90c3 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -142,7 +142,7 @@ void __weak arch_release_thread_info(struct thread_info *ti) { }
>   static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
>   						  int node)
>   {
> -	struct page *page = alloc_pages_node(node, THREADINFO_GFP,
> +	struct page *page = alloc_pages_node(node, THREADINFO_GFP_ACCOUNTED,
>   					     THREAD_SIZE_ORDER);
>   
>   	return page ? page_address(page) : NULL;
> @@ -151,7 +151,7 @@ static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
>   static inline void free_thread_info(struct thread_info *ti)
>   {
>   	arch_release_thread_info(ti);
> -	free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
> +	free_accounted_pages((unsigned long)ti, THREAD_SIZE_ORDER);
>   }
>   # else
>   static struct kmem_cache *thread_info_cache;
>