On Tue, 2016-05-10 at 13:34 +0800, Wanpeng Li wrote:
>
> +++ b/kernel/sched/cputime.c
>
> @@ -691,8 +691,11 @@ static cputime_t get_vtime_delta(struct
> task_struct *tsk)
>
> static void __vtime_account_system(struct task_struct *tsk)
> {
> + unsigned long steal_time = steal_account_process_tick();
> cputime_t delta_cpu = get_vtime_delta(tsk);
>
> + delta_cpu = steal_time ? (delta_cpu -
> + jiffies_to_cputime(steal_time)) : delta_cpu;
> account_system_time(tsk, irq_count(), delta_cpu,
> cputime_to_scaled(delta_cpu));
> }
> Sorry to have to go back on my previous email, but this is now a NAK The above code can end up passing a negative number to account_system_time(), which in turn can cause a divide by zero in scale_stime() The code needs to ensure that if all the time that passed was accounted as steal time (which could be more jiffies than expected, due to remaining partial jiffies in steal_account_process_tick), the function does not call account_system_time(). -- All Rights Reversed.
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