Re: [PATCH 1/2] rcu: Introduce force_rcu notifier

[Paolo Bonzini]

On 15/10/21 18:12, Greg Kurz wrote:
> +/*
> + * NotifierList used to force an RCU grace period.  Accessed under
> + * rcu_registry_lock.
> + */
> +static NotifierList force_rcu_notifiers =
> +    NOTIFIER_LIST_INITIALIZER(force_rcu_notifiers);
> +
>   /*
>    * Check whether a quiescent state was crossed between the beginning of
>    * update_counter_and_wait and now.
> @@ -107,6 +115,8 @@ static void wait_for_readers(void)
>                    * get some extra futex wakeups.
>                    */
>                   qatomic_set(&index->waiting, false);
> +            } else if (qatomic_read(&in_drain_call_rcu)) {
> +                notifier_list_notify(&force_rcu_notifiers, NULL);
>               }
>           }
>   

You can put the notifier in struct rcu_reader_data---this way it doesn't 
call all the notifiers but only those that are necessary to make progress.

While at it, I have a slight preference for a separate 
rcu_add_force_rcu_notifier API, but I can be convinced otherwise. :)

Paolo