Re: [RFC PATCH] sched, timer: Use atomics for thread_group_cputimer stats

[Peter Zijlstra]

On Thu, Jan 22, 2015 at 07:31:53PM -0800, Jason Low wrote:
> +static void update_gt_cputime(struct thread_group_cputimer *a, struct task_cputime *b)
>  {
> +	if (b->utime > atomic64_read(&a->utime))
> +		atomic64_set(&a->utime, b->utime);
>  
> +	if (b->stime > atomic64_read(&a->stime))
> +		atomic64_set(&a->stime, b->stime);
>  
> +	if (b->sum_exec_runtime > atomic64_read(&a->sum_exec_runtime))
> +		atomic64_set(&a->sum_exec_runtime, b->sum_exec_runtime);
>  }

See something like this is not safe against concurrent adds.
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