Re: [PATCH v2] oom: fix integer overflow of points in oom_badness

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

(10/31/2011 11:56 AM), Frantisek Hrbata wrote:
> An integer overflow will happen on 64bit archs if task's sum of rss, swapents
> and nr_ptes exceeds (2^31)/1000 value. This was introduced by commit
> 
> f755a04 oom: use pte pages in OOM score
> 
> where the oom score computation was divided into several steps and it's no
> longer computed as one expression in unsigned long(rss, swapents, nr_pte are
> unsigned long), where the result value assigned to points(int) is in
> range(1..1000). So there could be an int overflow while computing
> 
> 176          points *= 1000;
> 
> and points may have negative value. Meaning the oom score for a mem hog task
> will be one.
> 
> 196          if (points <= 0)
> 197                  return 1;
> 
> For example:
> [ 3366]     0  3366 35390480 24303939   5       0             0 oom01
> Out of memory: Kill process 3366 (oom01) score 1 or sacrifice child
> 
> Here the oom1 process consumes more than 24303939(rss)*4096~=92GB physical
> memory, but it's oom score is one.
> 
> In this situation the mem hog task is skipped and oom killer kills another and
> most probably innocent task with oom score greater than one.
> 
> The points variable should be of type long instead of int to prevent the int
> overflow.
> 
> Signed-off-by: Frantisek Hrbata <fhrbata@redhat.com>
> ---
>  mm/oom_kill.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 626303b..e9a1785 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -162,7 +162,7 @@ static bool oom_unkillable_task(struct task_struct *p,
>  unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem,
>  		      const nodemask_t *nodemask, unsigned long totalpages)
>  {
> -	int points;
> +	long points;
>  
>  	if (oom_unkillable_task(p, mem, nodemask))
>  		return 0;

Good catch.

Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>