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Commit 1b5ed5e1 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
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[BLOCK] cfq-iosched: cfq forced dispatching fix 



cfq forced dispatching might not return all requests on the queue.
This bug can hang elevator switchinig and corrupt request ordering
during flush sequence.

Signed-off-by: default avatarTejun Heo <htejun@gmail.com>
Signed-off-by: default avatarJens Axboe <axboe@suse.de>
parent 407df2aa

block/cfq-iosched.c

+45 −9
Original line number Diff line number Diff line
@@ -999,7 +999,7 @@ cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq) 
/*

 * get next queue for service

 */

static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd, int force)

static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)

{

	unsigned long now = jiffies;

	struct cfq_queue *cfqq;
@@ -1023,7 +1023,7 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd, int force) 
	 */

	if (!RB_EMPTY(&cfqq->sort_list))

		goto keep_queue;

	else if (!force && cfq_cfqq_class_sync(cfqq) &&

	else if (cfq_cfqq_class_sync(cfqq) &&

		 time_before(now, cfqq->slice_end)) {

		if (cfq_arm_slice_timer(cfqd, cfqq))

			return NULL;
@@ -1091,6 +1091,42 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq, 
	return dispatched;

}



static int

cfq_forced_dispatch_cfqqs(struct list_head *list)

{

	int dispatched = 0;

	struct cfq_queue *cfqq, *next;

	struct cfq_rq *crq;



	list_for_each_entry_safe(cfqq, next, list, cfq_list) {

		while ((crq = cfqq->next_crq)) {

			cfq_dispatch_insert(cfqq->cfqd->queue, crq);

			dispatched++;

		}

		BUG_ON(!list_empty(&cfqq->fifo));

	}

	return dispatched;

}



static int

cfq_forced_dispatch(struct cfq_data *cfqd)

{

	int i, dispatched = 0;



	for (i = 0; i < CFQ_PRIO_LISTS; i++)

		dispatched += cfq_forced_dispatch_cfqqs(&cfqd->rr_list[i]);



	dispatched += cfq_forced_dispatch_cfqqs(&cfqd->busy_rr);

	dispatched += cfq_forced_dispatch_cfqqs(&cfqd->cur_rr);

	dispatched += cfq_forced_dispatch_cfqqs(&cfqd->idle_rr);



	cfq_slice_expired(cfqd, 0);



	BUG_ON(cfqd->busy_queues);



	return dispatched;

}



static int

cfq_dispatch_requests(request_queue_t *q, int force)

{
@@ -1100,7 +1136,10 @@ cfq_dispatch_requests(request_queue_t *q, int force) 
	if (!cfqd->busy_queues)

		return 0;



	cfqq = cfq_select_queue(cfqd, force);

	if (unlikely(force))

		return cfq_forced_dispatch(cfqd);



	cfqq = cfq_select_queue(cfqd);

	if (cfqq) {

		int max_dispatch;
@@ -1115,12 +1154,9 @@ cfq_dispatch_requests(request_queue_t *q, int force) 
		cfq_clear_cfqq_wait_request(cfqq);

		del_timer(&cfqd->idle_slice_timer);



		if (!force) {

		max_dispatch = cfqd->cfq_quantum;

		if (cfq_class_idle(cfqq))

			max_dispatch = 1;

		} else

			max_dispatch = INT_MAX;



		return __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);

	}