On Mon, Aug 04, 2014 at 12:30:26PM +0200, Peter Zijlstra wrote:
> +long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
> +{
> + set_current_state(mode);
> + if (!(wait->flags & WQ_FLAG_WOKEN))
> + timeout = schedule_timeout(timeout);
> + else
> + wait->flags &= ~WQ_FLAG_WOKEN;
I just noticed that poll_schedule_timeout() uses set_mb() for clearing
its triggered variable. But I'm not entirely sure I see why..
> + __set_current_state(TASK_RUNNING);
> +
> + return timeout;
> +}
> +EXPORT_SYMBOL(wait_woken);
> +
> +int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void
> *key)
> +{
> + /*
> + * Although this function is called under waitqueue lock, LOCK
> + * doesn't imply write barrier and the users expect write
> + * barrier semantics on wakeup functions. The following
> + * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
> + * and is paired with set_mb() in wait_woken().
> + */
> + smp_wmb();
> + wait->flags |= WQ_FLAG_WOKEN;
> +
> + return default_wake_function(wait, mode, sync, key);
> +}
> +EXPORT_SYMBOL(woken_wake_function);
So possibly we could also use this for poll_schedule_timeout() and
__pollwake().
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