On Wed, Dec 11, 2013 at 08:06:37PM -0500, Paul Gortmaker wrote:
> +/* Adds w to head->task_list. Must be called with head->lock locked. */
> +static inline void __swait_enqueue(struct swait_queue_head *head,
> + struct swaiter *w)
> +{
> + list_add(&w->node, &head->task_list);
> + /* We can't let the condition leak before the setting of head */
> + smp_mb();
> +}
> +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;
> +}
Are these two barriers matched or are they both unmatched and thus
probabyl wrong?
In any case the comments need updating to be more explicit.
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