Re: [RESEND PATCH v9 tip/sched/core 1/6] sched: Annotate rq->rd with __rcu and update lockless readers

[Aaron Tomlin]

On Thu, Oct 29, 2026 at 09:25:06AM -0400, Aaron Tomlin wrote:
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 919d0fb00bd9..98a65d127e46 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -427,7 +427,7 @@ static bool build_perf_domains(const struct cpumask *cpu_map)
>  	int i;
>  	struct perf_domain *pd = NULL, *tmp;
>  	int cpu = cpumask_first(cpu_map);
> -	struct root_domain *rd = cpu_rq(cpu)->rd;
> +	struct root_domain *rd = rcu_dereference_root_domain(cpu_rq(cpu)->rd);
>  
>  	if (!sysctl_sched_energy_aware)
>  		goto free;
> @@ -492,9 +492,8 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
>  
>  	rq_lock_irqsave(rq, &rf);
>  
> -	if (rq->rd) {
> -		old_rd = rq->rd;
> -
> +	old_rd = rcu_dereference_root_domain(rq->rd);
> +	if (old_rd) {
>  		if (cpumask_test_cpu(rq->cpu, old_rd->online))
>  			set_rq_offline(rq);

  CHECK   kernel/sched/topology.c
[ ... ]
kernel/sched/topology.c:512:16: warning: incorrect type in assignment (different address spaces)
kernel/sched/topology.c:512:16:    expected struct root_domain [noderef] __rcu *rd
kernel/sched/topology.c:512:16:    got struct root_domain *rd

 512         rq->rd = rd;

We should use rcu_assign_pointer(rq->rd, rd) to resolve the Sparse
address-space warning. I will incorporate this change.

-- 
Aaron Tomlin