Re: [PATCH v7 13/22] sched: Allow task CPU affinity to be restricted on asymmetric systems

Peter Zijlstra
2021-05-26T17:25:05Z

On Tue, May 25, 2021 at 04:14:23PM +0100, Will Deacon wrote:
> +static int restrict_cpus_allowed_ptr(struct task_struct *p,
> + struct cpumask *new_mask,
> + const struct cpumask *subset_mask)
> +{
> + struct rq_flags rf;
> + struct rq *rq;
> + int err;
> + struct cpumask *user_mask = NULL;
> +
> + if (!p->user_cpus_ptr) {
> + user_mask = kmalloc(cpumask_size(), GFP_KERNEL);

if (!user_mask)
return -ENOMEM;
}

?

> +
> + rq = task_rq_lock(p, &rf);
> +
> + /*
> + * Forcefully restricting the affinity of a deadline task is
> + * likely to cause problems, so fail and noisily override the
> + * mask entirely.
> + */
> + if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
> + err = -EPERM;
> + goto err_unlock;
> + }
> +
> + if (!cpumask_and(new_mask, &p->cpus_mask, subset_mask)) {
> + err = -EINVAL;
> + goto err_unlock;
> + }
> +
> + /*
> + * We're about to butcher the task affinity, so keep track of what
> + * the user asked for in case we're able to restore it later on.
> + */
> + if (user_mask) {
> + cpumask_copy(user_mask, p->cpus_ptr);
> + p->user_cpus_ptr = user_mask;
> + }
> +
> + return __set_cpus_allowed_ptr_locked(p, new_mask, 0, rq, &rf);
> +
> +err_unlock:
> + task_rq_unlock(rq, p, &rf);
> + kfree(user_mask);
> + return err;
> +}