cfq-iosched: fix issue with rq-rq merging and fifo list ordering

cfq uses rq->start_time as the fifo indicator, but that field may
get modified prior to cfq doing it's fifo list adjustment when
a request gets merged with another request. This can cause the
fifo list to become unordered.

Reported-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9c4b679..e7f9e4e 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -827,8 +827,10 @@ cfq_merged_requests(struct request_queue *q, struct request *rq,
         * reposition in fifo if next is older than rq
         */
        if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
-           time_before(next->start_time, rq->start_time))
+           time_before(rq_fifo_time(next), rq_fifo_time(rq))) {
                list_move(&rq->queuelist, &next->queuelist);
+               rq_set_fifo_time(rq, rq_fifo_time(next));
+       }
 
        cfq_remove_request(next);
 }
@@ -1129,9 +1131,7 @@ static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
  */
 static struct request *cfq_check_fifo(struct cfq_queue *cfqq)
 {
-       struct cfq_data *cfqd = cfqq->cfqd;
-       struct request *rq;
-       int fifo;
+       struct request *rq = NULL;
 
        if (cfq_cfqq_fifo_expire(cfqq))
                return NULL;
@@ -1141,13 +1141,11 @@ static struct request *cfq_check_fifo(struct cfq_queue *cfqq)
        if (list_empty(&cfqq->fifo))
                return NULL;
 
-       fifo = cfq_cfqq_sync(cfqq);
        rq = rq_entry_fifo(cfqq->fifo.next);
-
-       if (time_before(jiffies, rq->start_time + cfqd->cfq_fifo_expire[fifo]))
+       if (time_before(jiffies, rq_fifo_time(rq)))
                rq = NULL;
 
-       cfq_log_cfqq(cfqd, cfqq, "fifo=%p", rq);
+       cfq_log_cfqq(cfqq->cfqd, cfqq, "fifo=%p", rq);
        return rq;
 }
 
@@ -2130,6 +2128,7 @@ static void cfq_insert_request(struct request_queue *q, struct request *rq)
 
        cfq_add_rq_rb(rq);
 
+       rq_set_fifo_time(rq, jiffies + cfqd->cfq_fifo_expire[rq_is_sync(rq)]);
        list_add_tail(&rq->queuelist, &cfqq->fifo);
 
        cfq_rq_enqueued(cfqd, cfqq, rq);