Messages in this thread | | | Date | Wed, 25 Oct 2023 10:40:08 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/4] rcu/tasks: Handle new PF_IDLE semantics |
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On Tue, Oct 24, 2023 at 11:46:23PM +0200, Frederic Weisbecker wrote:
> +/* Check for quiescent states since the pregp's synchronize_rcu() */ > +static bool rcu_tasks_is_holdout(struct task_struct *t) > +{ > + int cpu; > + > + /* Has the task been seen voluntarily sleeping? */ > + if (!READ_ONCE(t->on_rq)) > + return false; > + > + cpu = task_cpu(t); > + > + /* > + * Idle tasks within the idle loop or offline CPUs are RCU-tasks > + * quiescent states. But CPU boot code performed by the idle task > + * isn't a quiescent state. > + */ > + if (t == idle_task(cpu)) { > + if (is_idle_task(t)) > + return false; > + > + if (!rcu_cpu_online(cpu)) > + return false; > + }
Hmm, why is this guarded by t == idle_task() ?
Notably, there is the idle-injection thing that uses FIFO tasks to run 'idle', see play_idle_precise(). This will (temporarily) get PF_IDLE on tasks that are not idle_task().
> + > + return true; > +} > + > /* Per-task initial processing. */ > static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop) > { > - if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) { > + if (t != current && rcu_tasks_is_holdout(t)) {
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