On Thu, Dec 12, 2013 at 12:18:09PM +0100, Peter Zijlstra wrote:
> On Wed, Dec 11, 2013 at 08:06:37PM -0500, Paul Gortmaker wrote:
> > +unsigned int
> > +__swake_up_locked(struct swait_queue_head *head, unsigned int state,
> > + unsigned int num)
> > +{
> > + struct swaiter *curr, *next;
> > + int woken = 0;
> > +
> > + list_for_each_entry_safe(curr, next, &head->task_list, node) {
> > + if (wake_up_state(curr->task, state)) {
> > + __swait_dequeue(curr);
> > + /*
> > + * The waiting task can free the waiter as
> > + * soon as curr->task = NULL is written,
> > + * without taking any locks. A memory barrier
> > + * is required here to prevent the following
> > + * store to curr->task from getting ahead of
> > + * the dequeue operation.
> > + */
> > + smp_wmb();
> > + curr->task = NULL;
> > + if (++woken == num)
> > + break;
> > + }
> > + }
> > + return woken;
> > +}
> > +
> > +unsigned int
> > +__swake_up(struct swait_queue_head *head, unsigned int state, unsigned int
> > num)
> > +{
> > + unsigned long flags;
> > + int woken;
> > +
> > + if (!swaitqueue_active(head))
> > + return 0;
> > +
> > + raw_spin_lock_irqsave(&head->lock, flags);
> > + woken = __swake_up_locked(head, state, num);
> > + raw_spin_unlock_irqrestore(&head->lock, flags);
> > + return woken;
> > +}
> > +EXPORT_SYMBOL(__swake_up);
>
> Urgh, fail. Do not put unbounded loops in raw_spin_lock.
>
> I think I posted a patch a while back to cure this.
tada!
lkml.kernel.org/r/20131004145625.gn3...@twins.programming.kicks-ass.net
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