On Tue 18-09-12 18:04:10, 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 :(){ :|:& };:
OK. Although I was complaining that this is not the full truth the last
time, I do not insist on gravy details about the slaughter this will
cause to the rest of the group and that who-ever could fork in the group
can easily DOS the whole hierarchy. It has some interesting side effects
as well but let's keep this to a careful reader ;)
The patch, as is, is still useful and an improvement because it reduces
the impact.
>
> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
> Acked-by: Frederic Weisbecker <fweisbec@xxxxxxxxxx>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> CC: Christoph Lameter <cl@xxxxxxxxx>
> CC: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
> CC: Michal Hocko <mhocko@xxxxxxx>
> CC: Johannes Weiner <hannes@xxxxxxxxxxx>
> CC: Suleiman Souhlal <suleiman@xxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> 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 0ff2bf7..897e89c 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -146,7 +146,7 @@ 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;
> @@ -154,7 +154,7 @@ static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
>
> static inline void free_thread_info(struct 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;
> --
> 1.7.11.4
>
> --
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--
Michal Hocko
SUSE Labs
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