Re: [tip:sched/core] [sched/fair] c9d93a73ce: WARNING:suspicious_RCU_usage

[Andrea Righi]

Hello,

On Mon, May 25, 2026 at 09:53:22AM +0800, Chen, Yu C wrote:
> On 5/23/2026 9:27 PM, kernel test robot wrote:
> 
> > 
> > [  102.159951][   T23]
> > [  102.160730][   T23] =============================
> > [  102.162072][   T23] WARNING: suspicious RCU usage
> > [  102.163398][   T23] 7.1.0-rc2-00011-gc9d93a73ce87 #1 Not tainted
> > [  102.165064][   T23] -----------------------------
> > [  102.167687][   T23] kernel/sched/fair.c:12793 suspicious rcu_dereference_check() usage!
> > [  102.169994][   T23]

This should be fixed by
https://lore.kernel.org/all/20260522092523.2046095-1-arighi@xxxxxxxxxx/

Thanks,
-Andrea

> 
> sched_cpu_deactivate() does not hold RCU read lock, nor are
> preemption/IRQs/BH disabled,
> how about this:
>  static void set_cpu_sd_state_busy(int cpu)
>  {
>         struct sched_domain *sd;
> -       sd = rcu_dereference_all(per_cpu(sd_llc, cpu));
> +       sd = rcu_dereference_all_check(per_cpu(sd_llc, cpu),
> +                                      lockdep_is_cpus_held());
> 
>         /*
>          * sd->nohz_idle only pairs with nr_busy_cpus on sd->shared; if this
> @@ -12815,7 +12817,8 @@ void nohz_balance_exit_idle(struct rq *rq)
>  static void set_cpu_sd_state_idle(int cpu)
>  {
>         struct sched_domain *sd;
> -       sd = rcu_dereference_all(per_cpu(sd_llc, cpu));
> +       sd = rcu_dereference_all_check(per_cpu(sd_llc, cpu),
> +                                      lockdep_is_cpus_held());
> 
>         /* See set_cpu_sd_state_busy(): nohz_idle is only used with
> sd->shared. */
>         if (!sd || !sd->shared || sd->nohz_idle)