Re: [PATCH 20/25] sched/kcpustat: Introduce vtime-aware kcpustat accessor

Peter Zijlstra
2018-11-20T14:23:17Z

On Wed, Nov 14, 2018 at 03:46:04AM +0100, Frederic Weisbecker wrote:

> +void kcpustat_cputime(struct kernel_cpustat *kcpustat, int cpu,
> + u64 *user, u64 *nice, u64 *system,
> + u64 *guest, u64 *guest_nice)
> +{
> + struct task_struct *curr;
> + struct vtime *vtime;
> + int err;
> +
> + if (!vtime_accounting_enabled()) {
> + kcpustat_cputime_raw(kcpustat, user, nice,
> + system, guest, guest_nice);
> + return;
> + }
> +
> + rcu_read_lock();
> +
> + do {
> + curr = rcu_dereference(kcpustat->curr);

Like I explained earlier; I don't think the above is correct.
task_struct is itself not RCU protected.

> + if (!curr) {
> + kcpustat_cputime_raw(kcpustat, user, nice,
> + system, guest, guest_nice);
> + break;
> + }
> +
> + vtime = &curr->vtime;
> + err = kcpustat_vtime(kcpustat, vtime, cpu, user,
> + nice, system, guest, guest_nice);
> + } while (err == -EAGAIN);
> +
> + rcu_read_unlock();
> +}
> +
> #endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */
> --
> 2.7.4
>