On Tue, Sep 24, 2013 at 10:24:23PM +0200, Peter Zijlstra wrote:
> +void __get_online_cpus(void)
> +{
> + if (__cpuhp_writer == 1) {
take_ref:
> + /* See __srcu_read_lock() */
> + __this_cpu_inc(__cpuhp_refcount);
> + smp_mb();
> + __this_cpu_inc(cpuhp_seq);
> + return;
> + }
> +
> + atomic_inc(&cpuhp_waitcount);
> +
> /*
> + * We either call schedule() in the wait, or we'll fall through
> + * and reschedule on the preempt_enable() in get_online_cpus().
> */
> + preempt_enable_no_resched();
> + wait_event(cpuhp_readers, !__cpuhp_writer);
> + preempt_disable();
>
> + /*
> + * XXX list_empty_careful(&cpuhp_readers.task_list) ?
> + */
> + if (atomic_dec_and_test(&cpuhp_waitcount))
> + wake_up_all(&cpuhp_writer);
goto take_ref;
> +}
> +EXPORT_SYMBOL_GPL(__get_online_cpus);
It would probably be a good idea to increment __cpuhp_refcount after the
wait_event.
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