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

Peter Zijlstra
2015-01-23T09:25:14Z

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.