Re: [PATCH tip/core/rcu 22/30] rcu: Don't flag non-starting GPs before GP kthread is running

[Steven Rostedt]

On Fri, 14 Feb 2020 15:55:59 -0800
paulmck@xxxxxxxxxx wrote:

> @@ -1252,10 +1252,10 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
>   */
>  static void rcu_gp_kthread_wake(void)
>  {
> -	if ((current == rcu_state.gp_kthread &&
> +	if ((current == READ_ONCE(rcu_state.gp_kthread) &&
>  	     !in_irq() && !in_serving_softirq()) ||
>  	    !READ_ONCE(rcu_state.gp_flags) ||
> -	    !rcu_state.gp_kthread)
> +	    !READ_ONCE(rcu_state.gp_kthread))
>  		return;

This looks buggy. You have two instances of
READ_ONCE(rcu_state.gp_thread), which means they can be different. Is
that intentional?

-- Steve