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>

1 files changed, 7 insertions, 8 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9c4b679908f4..e7f9e4e3a270 100644
--- 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);