Re: [PATCH v5 3/3] cgroup/cpuset: Keep user set cpus affinity

[Tejun Heo]

On Tue, Aug 16, 2022 at 03:27:34PM -0400, Waiman Long wrote:
> +static int cpuset_set_cpus_allowed_ptr(struct task_struct *p,
> +				       const struct cpumask *mask)
> +{
> +	cpumask_var_t new_mask;
> +	int ret;
> +
> +	if (!READ_ONCE(p->user_cpus_ptr)) {
> +		ret = set_cpus_allowed_ptr(p, mask);
> +		/*
> +		 * If user_cpus_ptr becomes set now, we are racing with
> +		 * a concurrent sched_setaffinity(). So use the newly
> +		 * set user_cpus_ptr and retry again.
> +		 *
> +		 * TODO: We cannot detect change in the cpumask pointed to
> +		 * by user_cpus_ptr. We will have to add a sequence number
> +		 * if such a race needs to be addressed.
> +		 */

This is too ugly and obviously broken. Let's please do it properly.

Thanks.

-- 
tejun