Re: [patch 2/2] mm: memcg: do not allow task about to OOM kill tobypass the limit

[Michal Hocko]

On Wed 04-12-13 17:45:14, Johannes Weiner wrote:
> 4942642080ea ("mm: memcg: handle non-error OOM situations more
> gracefully") allowed tasks that already entered a memcg OOM condition
> to bypass the memcg limit on subsequent allocation attempts hoping
> this would expedite finishing the page fault and executing the kill.
> 
> David Rientjes is worried that this breaks memcg isolation guarantees
> and since there is no evidence that the bypass actually speeds up
> fault processing just change it so that these subsequent charge
> attempts fail outright.  The notable exception being __GFP_NOFAIL
> charges which are required to bypass the limit regardless.
> 
> Reported-by: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

We want this in stable as well IMHO.
Acked-by: Michal Hocko <mhocko@xxxxxxx>

> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f6a63f5b3827..bf5e89457149 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2694,7 +2694,7 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
>  		goto bypass;
>  
>  	if (unlikely(task_in_memcg_oom(current)))
> -		goto bypass;
> +		goto nomem;
>  
>  	if (gfp_mask & __GFP_NOFAIL)
>  		oom = false;
> -- 
> 1.8.4.2
> 

-- 
Michal Hocko
SUSE Labs
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