(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@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxx>
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