Re: [PATCH RFC] sched: introduce add_wait_queue_exclusive_head

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Mar 19, 2014 at 05:49:07PM +0100, Oleg Nesterov wrote:
> +static void add_wait_queue_flag(wait_queue_head_t *q, wait_queue_t *wait)
> +{
> +	struct list_head *head = &q->task_list;
> +	wait_queue_t *excl;
> +
> +	if (wait->flags & WQ_FLAG_EXCLUSIVE) {
> +		if (wait->flags & WQ_FLAG_EXCLUSIVE_HEAD) {
> +			list_for_each_entry(excl, head, task_list)
> +				if (excl->flags & WQ_FLAG_EXCLUSIVE) {
> +					head = &excl->task_list;
> +					break;
> +				}

I prefer an extra pair of { } here, but the main concern would be the
cost of that iteration.

> +		}
> +		/* turn list_add() below into list_add_tail() */
> +		head = head->prev;
> +	}
> +
> +	list_add(&wait->task_list, head);
> +}

Other than that, yes something like that would do I suppose.