On Wed, 14 Jan 2015 11:38:34 +0100
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
>
> So I had a look at this yesterday and came up with the below --
> completely untested etc.
>
> Now in order to compile test I meant to convert the completion code and
> ran head first into complete_all; it uses spin_lock_irqsave() which
> means it can be used from IRQ context. Now if you look at
> __swake_up_all() you'll find a comment on how we cannot have this.
>
> Now I can't remember how important that all was for RT but I figured I'd
> post it and let other people stare at it for a bit.
>
> +/*
> + * Does not allow usage from IRQ disabled, since we must be able to
> + * release IRQs to guarantee bounded hold time.
Actually we (-rt people) don't care if it's done with irq disabled, as
long is it was disabled via spin_lock_irq*() and not
raw_spin_lock_irq() or local_irq_save/disable().
Because in that case, in -rt, irqs would not be disabled. We could add a
check in -rt that makes sure that's the case. I would think this is OK
to call from an interrupt handler as long as it is a thread in -rt.
But, we can keep this restriction for now and change it if we find that
the restriction is preventing us from using it someplace where its
needed for -rt.
> + */
> +void __swake_up_all(struct swait_queue_head *q, unsigned int state)
> +{
> + struct swait_queue *curr, *next;
> + LIST_HEAD(tmp);
> +
> + __swait_wakeup_debug(q, state);
> +
> + if (!swait_active(q))
> + return;
> +
> + raw_spin_lock_irq(&q->lock);
> + list_splice_init(&q->task_list, &tmp);
> + while (!list_empty(&tmp)) {
> + curr = list_first_entry(&tmp, typeof(curr), task_list);
> +
> + wake_up_state(curr->task, state);
> + list_del_init(&curr->task_list);
What happens if curr->task does not match state? We just removed it
from the list and never woke it up, didn't we?
-- Steve
> +
> + if (list_empty(&tmp))
> + break;
> +
> + raw_spin_unlock_irq(&q->lock);
> + raw_spin_lock_irq(&q->lock);
> + }
> + raw_spin_unlock_irq(&q->lock);
> +}
> +EXPORT_SYMBOL(__swake_up_all);
> +
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